Erlang (/ˈɜːrlæŋ/ UR-lang) is a general-purpose, concurrent, functional programming language, and a garbage-collected runtime system. The term Erlang is used interchangeably with Erlang/OTP, or Open Telecom Platform (OTP), which consists of the Erlang runtime system, several ready-to-use components (OTP) mainly written in Erlang, and a set of design principles for Erlang programs.[3]

The Erlang runtime system is designed for systems with these traits:

Distributed Fault-tolerant Soft real-time Highly available, non-stop applications Hot swapping, where code can be changed without stopping a system.[4] The Erlang programming language has immutable data, pattern matching, and functional programming.[5] The sequential subset of the Erlang language supports eager evaluation, single assignment, and dynamic typing.

It was originally proprietary software within Ericsson, developed by Joe Armstrong, Robert Virding, and Mike Williams in 1986,[6] but was released as free and open-source software in 1998.[7][8] Erlang/OTP is supported and maintained by the Open Telecom Platform (OTP) product unit at Ericsson.

Contents 1 History 1.1 Processes 1.2 Usage 2 Functional programming examples 2.1 Factorial 2.2 Fibonacci sequence 2.3 Quicksort 3 Data types 4 "Let it Crash" coding style 4.1 Supervisor trees 5 Concurrency and distribution orientation 6 Implementation 7 Hot code loading and modules 8 Distribution 9 See also 10 References 11 Further reading 12 External links History The name Erlang, attributed to Bjarne Däcker, has been presumed by those working on the telephony switches (for whom the language was designed) to be a reference to Danish mathematician and engineer Agner Krarup Erlang and a syllabic abbreviation of "Ericsson Language".[6][9][clarification needed] Erlang was designed with the aim of improving the development of telephony applications. The initial version of Erlang was implemented in Prolog and was influenced by the programming language PLEX used in earlier Ericsson exchanges. By 1988 Erlang had proven that it was suitable for prototyping telephone exchanges, but the Prolog interpreter was far too slow. One group within Ericsson estimated that it would need to be 40 times faster to be suitable for production use. In 1992, work began on the BEAM virtual machine (VM) which compiles Erlang to C using a mix of natively compiled code and threaded code to strike a balance between performance and disk space.[10] According to Armstrong, the language went from lab product to real applications following the collapse of the next-generation AXE telephone exchange named AXE-N in 1995. As a result, Erlang was chosen for the next asynchronous transfer mode (ATM) exchange AXD.[6]

In 1998 Ericsson announced the AXD301 switch, containing over a million lines of Erlang and reported to achieve a high availability of nine "9"s.[11] Shortly thereafter, Ericsson Radio Systems banned the in-house use of Erlang for new products, citing a preference for non-proprietary languages. The ban caused Armstrong and others to leave Ericsson.[12] The implementation was open-sourced at the end of the year.[6] Ericsson eventually lifted the ban and re-hired Armstrong in 2004.[12]

In 2006, native symmetric multiprocessing support was added to the runtime system and VM.[6]

Processes Joe Armstrong, co-inventor of Erlang, summarized the principles of processes in his PhD thesis:[13]

Everything is a process. Processes are strongly isolated. Process creation and destruction is a lightweight operation. Message passing is the only way for processes to interact. Processes have unique names. If you know the name of a process you can send it a message. Processes share no resources. Error handling is non-local. Processes do what they are supposed to do or fail. Joe Armstrong remarked in an interview with Rackspace in 2013: "If Java is 'write once, run anywhere', then Erlang is 'write once, run forever'.”[14]

Usage In 2014, Ericsson reported Erlang was being used in its support nodes, and in GPRS, 3G and LTE mobile networks worldwide and also by Nortel and T-Mobile.[15]

As Tim Bray, director of Web Technologies at Sun Microsystems, expressed in his keynote at O'Reilly Open Source Convention (OSCON) in July 2008:

If somebody came to me and wanted to pay me a lot of money to build a large scale message handling system that really had to be up all the time, could never afford to go down for years at a time, I would unhesitatingly choose Erlang to build it in.

Erlang is the programming language used to code WhatsApp.[16]

Since being released as open source, Erlang has been spreading beyond Telecoms, establishing itself in other verticals such as FinTech, Gaming, Healthcare, Automotive, IoT and Blockchain. Apart from WhatsApp there are other companies listed as Erlang’s success stories:[17] Vocalink, a Mastercard company, Goldman Sachs, Nintendo, AdRoll, Grindr, BT Mobile, Samsung, OpenX, SITA.

Functional programming examples Factorial A factorial algorithm implemented in Erlang:

-module(fact). % This is the file 'fact.erl', the module and the filename must match -export([fac/1]). % This exports the function 'fac' of arity 1 (1 parameter, no type, no name)

fac(0) -> 1; % If 0, then return 1, otherwise (note the semicolon ; meaning 'else') fac(N) when N > 0, is_integer(N) -> N * fac(N-1). % Recursively determine, then return the result % (note the period . meaning 'endif' or 'function end') %% This function will crash if anything other than a nonnegative integer is given. %% It illustrates the "Let it crash" philosophy of Erlang. Fibonacci sequence A tail recursive algorithm that produces the Fibonacci sequence:

%% The module declaration must match the file name "series.erl" -module(series).

%% The export statement contains a list of all those functions that form %% the module's public API. In this case, this module exposes a single %% function called fib that takes 1 argument (I.E. has an arity of 1) %% The general syntax for -export is a list containing the name and %% arity of each public function -export([fib/1]).

%% --------------------------------------------------------------------- %% Public API %% ---------------------------------------------------------------------

%% Handle cases in which fib/1 receives specific values %% The order in which these function signatures are declared is a vital %% part of this module's functionality

%% If fib/1 is passed precisely the integer 0, then return 0 fib(0) -> 0;

%% If fib/1 receives a negative number, then return the atom err_neg_val %% Normally, such defensive coding is discouraged due to Erlang's 'Let %% it Crash' philosophy; however, in this case we should explicitly %% prevent a situation that will crash Erlang's runtime engine fib(N) when N < 0 -> err_neg_val;

%% If fib/1 is passed an integer less than 3, then return 1 %% The preceding two function signatures handle all cases where N < 1, %% so this function signature handles cases where N = 1 or N = 2 fib(N) when N < 3 -> 1;

%% For all other values, call the private function fib_int/3 to perform %% the calculation fib(N) -> fib_int(N, 0, 1).

%% --------------------------------------------------------------------- %% Private API %% ---------------------------------------------------------------------

%% If fibint/3 receives a 1 as its first argument, then we're done, so %% return the value in argument B. Since we are not interested in the %% value of the second argument, we denote this using to indicate a %% "don't care" value fibint(1, , B) -> B;

%% For all other argument combinations, recursively call fib_int/3 %% where each call does the following: %% - decrement counter N %% - Take the previous fibonacci value in argument B and pass it as %% argument A %% - Calculate the value of the current fibonacci number and pass it %% as argument B fib_int(N, A, B) -> fib_int(N-1, B, A+B). Here's the same program without the explanatory comments:

-module(series). -export([fib/1]).

fib(0) -> 0; fib(N) when N < 0 -> err_neg_val; fib(N) when N < 3 -> 1; fib(N) -> fib_int(N, 0, 1).

fibint(1, , B) -> B; fib_int(N, A, B) -> fib_int(N-1, B, A+B). Quicksort Quicksort in Erlang, using list comprehension:[18]

%% qsort:qsort(List) %% Sort a list of items -module(qsort). % This is the file 'qsort.erl' -export([qsort/1]). % A function 'qsort' with 1 parameter is exported (no type, no name)

qsort([]) -> []; % If the list [] is empty, return an empty list (nothing to sort) qsort([Pivot|Rest]) -> % Compose recursively a list with 'Front' for all elements that should be before 'Pivot' % then 'Pivot' then 'Back' for all elements that should be after 'Pivot' qsort([Front || Front <- Rest, Front < Pivot]) ++ [Pivot] ++ qsort([Back || Back <- Rest, Back >= Pivot]). The above example recursively invokes the function qsort until nothing remains to be sorted. The expression [Front || Front <- Rest, Front < Pivot] is a list comprehension, meaning "Construct a list of elements Front such that Front is a member of Rest, and Front is less than Pivot." ++ is the list concatenation operator.

A comparison function can be used for more complicated structures for the sake of readability.

The following code would sort lists according to length:

% This is file 'listsort.erl' (the compiler is made this way) -module(listsort). % Export 'by_length' with 1 parameter (don't care about the type and name) -export([by_length/1]).

by_length(Lists) -> % Use 'qsort/2' and provides an anonymous function as a parameter qsort(Lists, fun(A,B) -> length(A) < length(B) end).

qsort([], _)-> []; % If list is empty, return an empty list (ignore the second parameter) qsort([Pivot|Rest], Smaller) -> % Partition list with 'Smaller' elements in front of 'Pivot' and not-'Smaller' elements % after 'Pivot' and sort the sublists. qsort([X || X <- Rest, Smaller(X,Pivot)], Smaller) ++ [Pivot] ++ qsort([Y || Y <- Rest, not(Smaller(Y, Pivot))], Smaller). A Pivot is taken from the first parameter given to qsort() and the rest of Lists is named Rest. Note that the expression

[X || X <- Rest, Smaller(X,Pivot)] is no different in form from

[Front || Front <- Rest, Front < Pivot] (in the previous example) except for the use of a comparison function in the last part, saying "Construct a list of elements X such that X is a member of Rest, and Smaller is true", with Smaller being defined earlier as

fun(A,B) -> length(A) < length(B) end The anonymous function is named Smaller in the parameter list of the second definition of qsort so that it can be referenced by that name within that function. It is not named in the first definition of qsort, which deals with the base case of an empty list and thus has no need of this function, let alone a name for it.

Data types Erlang has eight primitive data types:

Integers Integers are written as sequences of decimal digits, for example, 12, 12375 and -23427 are integers. Integer arithmetic is exact and only limited by available memory on the machine. (This is called arbitrary-precision arithmetic.) Atoms Atoms are used within a program to denote distinguished values. They are written as strings of consecutive alphanumeric characters, the first character being lowercase. Atoms can contain any character if they are enclosed within single quotes and an escape convention exists which allows any character to be used within an atom. Atoms are never garbage collected and should be used with caution, especially if using dynamic atom generation. Floats Floating point numbers use the IEEE 754 64-bit representation. References References are globally unique symbols whose only property is that they can be compared for equality. They are created by evaluating the Erlang primitive make_ref(). Binaries A binary is a sequence of bytes. Binaries provide a space-efficient way of storing binary data. Erlang primitives exist for composing and decomposing binaries and for efficient input/output of binaries. Pids Pid is short for process identifier – a Pid is created by the Erlang primitive spawn(...) Pids are references to Erlang processes. Ports Ports are used to communicate with the external world. Ports are created with the built-in function open_port. Messages can be sent to and received from ports, but these messages must obey the so-called "port protocol." Funs Funs are function closures. Funs are created by expressions of the form: fun(...) -> ... end. And three compound data types:

Tuples Tuples are containers for a fixed number of Erlang data types. The syntax {D1,D2,...,Dn} denotes a tuple whose arguments are D1, D2, ... Dn. The arguments can be primitive data types or compound data types. Any element of a tuple can be accessed in constant time. Lists Lists are containers for a variable number of Erlang data types. The syntax [Dh|Dt] denotes a list whose first element is Dh, and whose remaining elements are the list Dt. The syntax [] denotes an empty list. The syntax [D1,D2,..,Dn] is short for [D1|[D2|..|[Dn|[]]]]. The first element of a list can be accessed in constant time. The first element of a list is called the head of the list. The remainder of a list when its head has been removed is called the tail of the list. Maps Maps contain a variable number of key-value associations. The syntax is#{Key1=>Value1,...,KeyN=>ValueN}. Two forms of syntactic sugar are provided:

Strings Strings are written as doubly quoted lists of characters. This is syntactic sugar for a list of the integer Unicode code points for the characters in the string. Thus, for example, the string "cat" is shorthand for [99,97,116].[19] Records Records provide a convenient way for associating a tag with each of the elements in a tuple. This allows one to refer to an element of a tuple by name and not by position. A pre-compiler takes the record definition and replaces it with the appropriate tuple reference. Erlang has no method to define classes, although there are external libraries available.[20]

"Let it Crash" coding style In most other programming languages, software crashes have always been (and often still are) considered highly undesirable situations that must be avoided at all costs. Consequently, elaborate exception handling mechanisms exist to trap these situations and then mitigate their effects. This design philosophy exists because many of the foundational principles of software design were defined at a time when computers were single processor machines. Under these conditions, software crashes were indeed fatal. Given this basic constraint, it was perfectly natural therefore to develop programming styles in which a large proportion of the code was dedicated to detecting and then handling error situations. This in turn, led directly to the still widely popular coding style known as defensive programming.

However, the designers of Erlang realised that in spite of their undesirable effects, software crashes are much like death and taxes - quite unavoidable. Therefore, rather than treating a crash as a crisis situation that temporarily suspends all normal work until a solution is found, they reasoned it would make far greater sense to treat a crash in exactly the same manner as any other normal runtime event. Consequently, when an Erlang process crashes, this situation is reported as just another type of message arriving in a process' mail box.

This realisation led to Erlang's designers building a language with the following fundamental features:

Erlang has no concept of global memory; therefore relative to each other, all processes are isolated execution environments Erlang processes can: be spawned very cheaply only communicate using message passing monitor each other. This allows processes to be arranged in hierarchies known as "supervisor trees." A process should perform its task or fail Process failure is reported simply as a message The "Let it Crash" style of coding is therefore the practical consequence of working in a language that operates on these principles.

Supervisor trees A typical Erlang application is written in the form of a supervisor tree. This architecture is based on a hierarchy of processes in which the top level process is known as a "supervisor". The supervisor then spawns multiple child processes that act either as workers or more, lower level supervisors. Such hierarchies can exist to arbitrary depths and have proven to provide a highly scalable and fault-tolerant environment within which application functionality can be implemented.

Within a supervisor tree, all supervisor processes are responsible for managing the lifecycle of their child processes, and this includes handling situations in which those child processes crash. Any process can become a supervisor by first spawning a child process, then calling erlang:monitor/2 on that process. If the monitored process then crashes, the supervisor will receive a message containing a tuple whose first member is the atom 'DOWN'. The supervisor is responsible firstly for listening for such messages and secondly, for taking the appropriate action to correct the error condition.

In addition, "Let it Crash" results in a style of coding that contains little defensive code, resulting in smaller applications.

Concurrency and distribution orientation Erlang's main strength is support for concurrency. It has a small but powerful set of primitives to create processes and communicate among them. Erlang is conceptually similar to the language occam, though it recasts the ideas of communicating sequential processes (CSP) in a functional framework and uses asynchronous message passing.[21] Processes are the primary means to structure an Erlang application. They are neither operating system processes nor threads, but lightweight processes that are scheduled by BEAM. Like operating system processes (but unlike operating system threads), they share no state with each other. The estimated minimal overhead for each is 300 words.[22] Thus, many processes can be created without degrading performance. In 2005, a benchmark with 20 million processes was successfully performed with 64-bit Erlang on a machine with 16 GB random-access memory (RAM; total 800 bytes/process).[23] Erlang has supported symmetric multiprocessing since release R11B of May 2006.

While threads need external library support in most languages, Erlang provides language-level features to create and manage processes with the goal of simplifying concurrent programming. Though all concurrency is explicit in Erlang, processes communicate using message passing instead of shared variables, which removes the need for explicit locks (a locking scheme is still used internally by the VM).[24]

Inter-process communication works via a shared-nothing asynchronous message passing system: every process has a "mailbox", a queue of messages that have been sent by other processes and not yet consumed. A process uses the receive primitive to retrieve messages that match desired patterns. A message-handling routine tests messages in turn against each pattern, until one of them matches. When the message is consumed and removed from the mailbox the process resumes execution. A message may comprise any Erlang structure, including primitives (integers, floats, characters, atoms), tuples, lists, and functions.

The code example below shows the built-in support for distributed processes:

% Create a process and invoke the function web:start_server(Port, MaxConnections) ServerProcess = spawn(web, start_server, [Port, MaxConnections]),

% Create a remote process and invoke the function % web:start_server(Port, MaxConnections) on machine RemoteNode RemoteProcess = spawn(RemoteNode, web, start_server, [Port, MaxConnections]),

% Send a message to ServerProcess (asynchronously). The message consists of a tuple % with the atom "pause" and the number "10". ServerProcess ! {pause, 10},

% Receive messages sent to this process receive a_message -> do_something; {data, DataContent} -> handle(DataContent); {hello, Text} -> io:format("Got hello message: ~s", [Text]); {goodbye, Text} -> io:format("Got goodbye message: ~s", [Text]) end. As the example shows, processes may be created on remote nodes, and communication with them is transparent in the sense that communication with remote processes works exactly as communication with local processes.

Concurrency supports the primary method of error-handling in Erlang. When a process crashes, it neatly exits and sends a message to the controlling process which can then take action, such as for instance starting a new process that takes over the old process's task.[25][26]

Implementation The official reference implementation of Erlang uses BEAM.[27] BEAM is included in the official distribution of Erlang, called Erlang/OTP. BEAM executes bytecode which is converted to threaded code at load time. It also includes a native code compiler on most platforms, developed by the High Performance Erlang Project (HiPE) at Uppsala University. Since October 2001 the HiPE system is fully integrated in Ericsson's Open Source Erlang/OTP system.[28] It also supports interpreting, directly from source code via abstract syntax tree, via script as of R11B-5 release of Erlang.

Hot code loading and modules Erlang supports language-level Dynamic Software Updating. To implement this, code is loaded and managed as "module" units; the module is a compilation unit. The system can keep two versions of a module in memory at the same time, and processes can concurrently run code from each. The versions are referred to as the "new" and the "old" version. A process will not move into the new version until it makes an external call to its module.

An example of the mechanism of hot code loading:

%% A process whose only job is to keep a counter. %% First version -module(counter). -export([start/0, codeswitch/1]).

start() -> loop(0).

loop(Sum) -> receive {increment, Count} -> loop(Sum+Count); {counter, Pid} -> Pid ! {counter, Sum}, loop(Sum); code_switch -> ?MODULE:codeswitch(Sum) % Force the use of 'codeswitch/1' from the latest MODULE version end.

codeswitch(Sum) -> loop(Sum). For the second version, we add the possibility to reset the count to zero.

%% Second version -module(counter). -export([start/0, codeswitch/1]).

start() -> loop(0).

loop(Sum) -> receive {increment, Count} -> loop(Sum+Count); reset -> loop(0); {counter, Pid} -> Pid ! {counter, Sum}, loop(Sum); code_switch -> ?MODULE:codeswitch(Sum) end.

codeswitch(Sum) -> loop(Sum). Only when receiving a message consisting of the atom code_switch will the loop execute an external call to codeswitch/1 (?MODULE is a preprocessor macro for the current module). If there is a new version of the counter module in memory, then its codeswitch/1 function will be called. The practice of having a specific entry-point into a new version allows the programmer to transform state to what is needed in the newer version. In the example, the state is kept as an integer.

In practice, systems are built up using design principles from the Open Telecom Platform, which leads to more code upgradable designs. Successful hot code loading is exacting. Code must be written with care to make use of Erlang's facilities.

Distribution In 1998, Ericsson released Erlang as free and open-source software to ensure its independence from a single vendor and to increase awareness of the language. Erlang, together with libraries and the real-time distributed database Mnesia, forms the OTP collection of libraries. Ericsson and a few other companies support Erlang commercially.

Since the open source release, Erlang has been used by several firms worldwide, including Nortel and T-Mobile.[29] Although Erlang was designed to fill a niche and has remained an obscure language for most of its existence, its popularity is growing due to demand for concurrent services.[30][31] Erlang has found some use in fielding massively multiplayer online role-playing game (MMORPG) servers.[32]

See also Elixir – a functional, concurrent, general-purpose programming language that runs on BEAM Lisp Flavored Erlang (LFE) – a Lisp-based programming language that runs on BEAM Mix (build tool) Phoenix (web framework)

Go

Go is a statically typed, compiled programming language designed at Google[14] by Robert Griesemer, Rob Pike, and Ken Thompson. [12] Go is syntactically similar to C, but with memory safety, garbage collection, structural typing, [6] and CSP-style concurrency. [15] The language is often referred to as "Golang" because of its domain name, golang.org, but the proper name is Go.[16] There are two major implementations: Google's self-hosting[17] compiler toolchain targeting multiple operating systems, mobile devices,[18] and WebAssembly. [19] gccgo, a GCC frontend.[20][21] A third-party transpiler GopherJS[22] compiles Go to JavaScript for front-end web development. History Version history Design Syntax Types Interface system Package system Concurrency: goroutines and channels Suitability for parallel programming Lack of race condition safety Binaries Omissions Style Tools Examples Hello world Concurrency Testing Editing environments Applications Reception Contents gc, gccgo Influenced by Alef, APL, [11] BCPL, [11] C, CSP, Limbo, Modula, Newsqueak, Oberon, occam, Pascal, [12] Smalltalk [13] Influenced Crystal Gopher mascot Naming dispute Criticism See also Notes References Further reading External links Go was designed at Google in 2007 to improve programming productivity in an era of multicore, networked machines and large codebases. [23] The designers wanted to address criticism of other languages in use at Google, but keep their useful characteristics:[24] static typing and run-time efficiency (like C++), readability and usability (like Python or JavaScript),[25] high-performance networking and multiprocessing. The designers were primarily motivated by their shared dislike of C++. [26][27][28] Go was publicly announced in November 2009,[29] and version 1.0 was released in March 2012.[30][31] Go is widely used in production at Google[32] and in many other organizations and open-source projects. In November 2016, the Go and Go Mono fonts were released by type designers Charles Bigelow and Kris Holmes specifically for use by the Go project. Go and Go Mono fonts are sans-serif and monospaced respectively. Both fonts adhere to WGL4 and were designed to be legible, with a large x-height and distinct letterforms, by conforming to the DIN 1450 standard.[33][34] In April 2018, the original logo was replaced with a stylized GO slanting right with trailing streamlines. However, the Gopher mascot remained the same.[35] In August 2018, the Go principal contributors published two "draft designs" for new language features, Generics and error handling, and asked Go users to submit feedback on them.[36][37] Lack of support for generic programming and the verbosity of error handling in Go 1.x had drawn considerable criticism. Go 1 guarantees compatibility[38] for the language specification and major parts of the standard library. All versions up to the current Go 1.12 release[39] have maintained this promise. Each major Go release is supported until there are two newer major releases.[40] History Version history Version history of Go Major version Initial release date Language changes [41] Other changes 1–1.0.3 2012- 03-28 Initial release 1.1– 1.1.2 2013- 05-13 In Go 1.1, an integer division by constant zero is not a legal program, so it is a compiletime error. The definition of string and rune literals has been refined to exclude surrogate halves from the set of valid Unicode code points. Loosened return requirements rules. If the compiler can prove that a function always returns before reaching the end of a function, a final terminating statement can be omitted. The language allows the implementation to choose whether the int type and uint types are 32 or 64 bits. On 64-bit architectures, the maximum heap size has been enlarged substantially, from a few gigabytes to several tens of gigabytes. Addition of a race detector to the standard tool set. 1.2– 1.2.2 2013- 12-01 The language now specifies that, for safety reasons, certain uses of nil pointers are guaranteed to trigger a runtime panic. Go 1.2 adds the ability to specify the capacity as well as the length when using a slicing operation on an existing array or slice. A slicing operation creates a new slice by describing a contiguous section of an already-created array or slice. The runtime scheduler can now be invoked on (noninlined) function calls. Go 1.2 introduces a configurable limit (default 10,000) to the total number of threads a single program may have. In Go 1.2, the minimum size of the stack when a goroutine is created has been lifted from 4KB to 8KB. 1.3– 1.3.3 2014- 06-18 There are no language changes in this release. The Go 1.3 memory model adds a new rule concerning sending and receiving on buffered channels, to make explicit that a buffered channel can be used as a simple semaphore, using a send into the channel to acquire and a receive from the channel to release. Go 1.3 has changed the implementation of goroutine stacks away from the old, "segmented" model to a contiguous model. For a while now, the garbage collector has been precise when examining values in the heap; the Go 1.3 release adds equivalent precision to values on the stack. Iterations over small maps no longer happen in a consistent order. This is due to developers abusing implementation behaviour. 1.4– 1.4.3 2014- 12-10 Range-expression without assignment Automatic double-dereference on method calls is now In 1.4, much of the runtime code has been translated to Go so that the garbage collector can scan the stacks of programs in the runtime and get accurate information about what variables are active. disallowed in gc and gccgo. This is a backwards incompatible change, but in line with the language specification. The language accepted by the assemblers cmd/5a, cmd/6a and cmd/8a has had several changes, mostly to make it easier to deliver type information to the runtime. Addition of internal packages. New subcommand go generate. 1.5– 1.5.4 2015- 08-19 Due to an oversight, the rule that allowed the element type to be elided from slice literals was not applied to map keys. This has been corrected in Go 1.5. The compiler and runtime are now implemented in Go and assembler, without C. Now that the Go compiler and runtime are implemented in Go, a Go compiler must be available to compile the distribution from source. The compiler is now self-hosted. The garbage collector has been re-engineered for 1.5. The "stop the world" phase of the collector will almost always be under 10 milliseconds and usually much less. In Go 1.5, the order in which goroutines are scheduled has been changed. 1.6– 1.6.4 2016- 02-17 There are no language changes in this release. A major change was made to cgo defining the rules for sharing Go pointers with C code, to ensure that such C code can coexist with Go's garbage collector. The Go parser is now hand-written instead of generated. The go vet command now diagnoses passing function or method values as arguments to Printf, such as when passing f where f() was intended. 1.7– 1.7.6 2016- 08-15 Clarification on terminating statements in the language specification. This does not change existing behaviour. For 64-bit x86 systems, the following instructions have been added (see SSE): PCMPESTRI, RORXL, RORXQ, VINSERTI128, VPADDD, VPADDQ, VPALIGNR, VPBLENDD, VPERM2F128, VPERM2I128, VPOR, VPSHUFB, VPSHUFD, VPSLLD, VPSLLDQ, VPSLLQ, VPSRLD, VPSRLDQ, and VPSRLQ . This release includes a new code generation back end for 64-bit x86 systems, based on SSA. Packages using cgo may now include Fortran source files (in addition to C, C++, Objective C, and SWIG), although the Go bindings must still use C language APIs. The new subcommand “go tool dist list” prints all supported operating system/architecture pairs. 1.8– 1.8.7 2017- 02-16 When explicitly converting a value from one struct type to another, as of Go 1.8 the tags are ignored. Thus two structs that differ only in their tags may be converted from one to the other. For 64-bit x86 systems, the following instructions have been added: VBROADCASTSD, BROADCASTSS, MOVDDUP, MOVSHDUP, MOVSLDUP, VMOVDDUP, VMOVSHDUP, and VMOVSLDUP. Garbage collection pauses should be significantly shorter than they were in Go 1.7, usually under 100 microseconds and often as low as 10 microseconds. See the document on eliminating stop-the-world stack re-scanning for details. The overhead of deferred function calls has been reduced by about half. The overhead of calls from Go into C has been reduced by about half. 1.9– 1.9.7 2017- 08-24 Go now supports type aliases. Force the intermediate rounding in floating-point arithmetic. The Go compiler now supports compiling a package's functions in parallel, taking advantage of multiple cores. 1.10– 1.10.7 2018- 02-16 A corner case involving shifts of untyped constants has been clarified. The grammar for method expressions has been updated to relax the syntax to allow any type expression as a receiver. For the x86 64-bit port, the assembler now supports 359 new instructions, including the full AVX, AVX2, BMI, BMI2, F16C, FMA3, SSE2, SSE3, SSSE3, SSE4.1, and SSE4.2 extension sets. The assembler also no longer implements MOVL $0, AX as an XORL instruction, to avoid clearing the condition flags unexpectedly. 1.11– 1.11.6 2018- 08-24 There are no changes to the language specification. Go 1.11 adds an experimental port to WebAssembly. Go 1.11 adds preliminary support for a new concept called “modules”, an alternative to GOPATH with integrated support for versioning and package distribution. The assembler for amd64 now accepts AVX512 instructions. Go 1.11 drops support of Windows XP and Windows Vista. [42] Go 1.11.3 and later fix the TLS authentication vulnerability in the crypto/x509 package. [43] 1.12.1 2019- 02-25 There are no changes to the language specification. Opt-in support for TLS 1.3 Improved modules support (in preparation for being the default in Go 1.13) Support for windows/arm Improved macOS & iOS forwards compatibility 1.13.1 2019- 09-03 Go now supports a more uniform and modernized set of number literal prefixes support for TLS 1.3 in the crypto/tls package by default (opt-out will be removed in Go 1.14) Support for error wrapping 1.14 2020- 02-25 Permits embedding interfaces with overlapping method sets[44] Module support in the go command is now ready for production use[45] Go is influenced by C, but with an emphasis on greater simplicity and safety. The language consists of: A syntax and environment adopting patterns more common in dynamic languages: [46] Optional concise variable declaration and initialization through type inference (x := 0 instead of int x = 0; or var x = 0;). Fast compilation.[47] Design Remote package management (go get) [48] and online package documentation.[49] Distinctive approaches to particular problems: Built-in concurrency primitives: light-weight processes (goroutines), channels, and the select statement. An interface system in place of virtual inheritance, and type embedding instead of nonvirtual inheritance. A toolchain that, by default, produces statically linked native binaries without external dependencies. A desire to keep the language specification simple enough to hold in a programmer's head,[50] in part by omitting features that are common in similar languages. Go's syntax includes changes from C aimed at keeping code concise and readable. A combined declaration/initialization operator was introduced that allows the programmer to write i := 3 or s := "Hello, world!", without specifying the types of variables used. This contrasts with C's int i = 3; and const char s = "Hello, world!";. Semicolons still terminate statements,[a] but are implicit when the end of a line occurs.[b] Methods may return multiple values, and returning a result, err pair is the conventional way a method indicates an error to its caller in Go.[c] Go adds literal syntaxes for initializing struct parameters by name and for initializing maps and slices. As an alternative to C's threestatement for loop, Go's range expressions allow concise iteration over arrays, slices, strings, maps, and channels. Go has a number of built-in types, including numeric ones (byte, int64, float32, etc.), booleans, and character strings (string). Strings are immutable; built-in operators and keywords (rather than functions) provide concatenation, comparison, and UTF-8 encoding/decoding.[53] Record types can be defined with the struct keyword.[54] For each type T and each non-negative integer constant n, there is an array type denoted [n]T; arrays of differing lengths are thus of different types. Dynamic arrays are available as "slices", denoted []T for some type T. These have a length and a capacity specifying when new memory needs to be allocated to expand the array. Several slices may share their underlying memory. [55][56][57] Pointers are available for all types, and the pointer-to-T type is denoted T. Address-taking and indirection use the & and * operators, as in C, or happen implicitly through the method call or attribute access syntax.[58] There is no pointer arithmetic,[d] except via the special unsafe.Pointer type in the standard library. [59] For a pair of types K, V, the type map[K]V is the type of hash tables mapping type-K keys to type-V values. Hash tables are built into the language, with special syntax and built-in functions. chan T is a channel that allows sending values of type T between concurrent Go processes. Aside from its support for interfaces, Go's type system is nominal: the type keyword can be used to define a new named type, which is distinct from other named types that have the same layout (in the case of a struct, the same members in the same order). Some conversions between types (e.g., between the various Syntax Types integer types) are pre-defined and adding a new type may define additional conversions, but conversions between named types must always be invoked explicitly. [60] For example, the type keyword can be used to define a type for IPv4 addresses, based on 32-bit unsigned integers: type ipv4addr uint32 With this type definition, ipv4addr(x) interprets the uint32 value x as an IP address. Simply assigning x to a variable of type ipv4addr is a type error. Constant expressions may be either typed or "untyped"; they are given a type when assigned to a typed variable if the value they represent passes a compile-time check.[61] Function types are indicated by the func keyword; they take zero or more parameters and return zero or more values, all of which are typed. The parameter and return values determine a function type; thus, func(string, int32) (int, error) is the type of functions that take a string and a 32-bit signed integer, and return a signed integer (of default width) and a value of the built-in interface type error. Any named type has a method set associated with it. The IP address example above can be extended with a method for checking whether its value is a known standard: // ZeroBroadcast reports whether addr is 255.255.255.255. func (addr ipv4addr) ZeroBroadcast() bool { return addr == 0xFFFFFFFF } Due to nominal typing, this method definition adds a method to ipv4addr, but not on uint32. While methods have special definition and call syntax, there is no distinct method type.[62] Go provides two features that replace class inheritance. The first is embedding, which can be viewed as an automated form of composition[63] or delegation.

The second are its interfaces, which provides runtime polymorphism.

Interfaces are a class of types and provide a limited form of structural typing in the otherwise nominal type system of Go. An object which is of an interface type is also of another type, much like C++ objects being simultaneously of a base and derived class. Go interfaces were designed after protocols from the Smalltalk programming language.[66] Multiple sources use the term duck typing when describing Go interfaces.[67][68] Although the term duck typing is not precisely defined and therefore not wrong, it usually implies that type conformance is not statically checked. Since conformance to a Go interface is checked statically by the Go compiler (except when performing a type assertion), the Go authors prefer the term structural typing. [69] The definition of an interface type lists required methods by name and type. Any object of type T for which functions exist matching all the required methods of interface type I is an object of type I as well. The definition of type T need not (and cannot) identify type I. For example, if Shape, Square and Circle are defined as import "math" type Shape interface { Interface system Area() float64 } type Square struct { // Note: no "implements" declaration side float64 } func (sq Square) Area() float64 { return sq.side sq.side } type Circle struct { // No "implements" declaration here either radius float64 } func (c Circle) Area() float64 { return math.Pi math.Pow(c.radius, 2) } then both a Square and a Circle are implicitly a Shape and can be assigned to a Shape-typed variable.65:263–268 In formal language, Go's interface system provides structural rather than nominal typing. Interfaces can embed other interfaces with the effect of creating a combined interface that is satisfied by exactly the types that implement the embedded interface and any methods that the newly defined interface adds.65:270 The Go standard library uses interfaces to provide genericity in several places, including the input/output system that is based on the concepts of Reader and Writer.

Besides calling methods via interfaces, Go allows converting interface values to other types with a run-time type check. The language constructs to do so are the type assertion, [70] which checks against a single potential type, and the type switch, [71] which checks against multiple types. The empty interface interface{} is an important base case because it can refer to an item of any concrete type. It is similar to the Object class in Java or C# and is satisfied by any type, including built-in types like int. 65:284 Code using the empty interface cannot simply call methods (or built-in operators) on the referred-to object, but it can store the interface{} value, try to convert it to a more useful type via a type assertion or type switch, or inspect it with Go's reflect package.[72] Because interface{} can refer to any value, it is a limited way to escape the restrictions of static typing, like void* in C but with additional run-time type checks. Interface values are implemented using pointer to data and a second pointer to run-time type information.[73] Like some other types implemented using pointers in Go, interface values are nil if uninitialized.[74] In Go's package system, each package has a path (e.g., "compress/bzip2" or "golang.org/x/net/html") and a name (e.g., bzip2 or html). References to other packages' definitions must always be prefixed with the other package's name, and only the capitalized names from other packages are accessible: io.Reader is public but bzip2.reader is not.[75] The go get command can retrieve packages stored in a remote repository [76] and developers are encouraged to develop packages inside a base path corresponding to a source repository (such as example.com/user_name/package_name) to reduce the likelihood of name collision with future additions to the standard library or other external libraries.[77] Proposals exist to introduce a proper package management solution for Go similar to CPAN for Perl or Rust's cargo system or Node's npm system.[78] Package system Concurrency: goroutines and channels The Go language has built-in facilities, as well as library support, for writing concurrent programs. Concurrency refers not only to CPU parallelism, but also to asynchrony: letting slow operations like a database or network read run while the program does other work, as is common in event-based servers.[79] The primary concurrency construct is the goroutine, a type of light-weight process. A function call prefixed with the go keyword starts a function in a new goroutine. The language specification does not specify how goroutines should be implemented, but current implementations multiplex a Go process's goroutines onto a smaller set of operating-system threads, similar to the scheduling performed in Erlang.

While a standard library package featuring most of the classical concurrency control structures (mutex locks, etc.) is available,80:151–152 idiomatic concurrent programs instead prefer channels, which provide send messages between goroutines.[81] Optional buffers store messages in FIFO order64:43 and allow sending goroutines to proceed before their messages are received. Channels are typed, so that a channel of type chan T can only be used to transfer messages of type T. Special syntax is used to operate on them; <-ch is an expression that causes the executing goroutine to block until a value comes in over the channel ch, while ch <- x sends the value x (possibly blocking until another goroutine receives the value). The built-in switch-like select statement can be used to implement non-blocking communication on multiple channels; see below for an example. Go has a memory model describing how goroutines must use channels or other operations to safely share data.[82] The existence of channels sets Go apart from actor model-style concurrent languages like Erlang, where messages are addressed directly to actors (corresponding to goroutines). The actor style can be simulated in Go by maintaining a one-to-one correspondence between goroutines and channels, but the language allows multiple goroutines to share a channel or a single goroutine to send and receive on multiple channels.80:147 From these tools one can build concurrent constructs like worker pools, pipelines (in which, say, a file is decompressed and parsed as it downloads), background calls with timeout, "fan-out" parallel calls to a set of services, and others.[83] Channels have also found uses further from the usual notion of interprocess communication, like serving as a concurrency-safe list of recycled buffers,[84] implementing coroutines (which helped inspire the name goroutine),[85] and implementing iterators. [86] Concurrency-related structural conventions of Go (channels and alternative channel inputs) are derived from Tony Hoare's communicating sequential processes model. Unlike previous concurrent programming languages such as Occam or Limbo (a language on which Go co-designer Rob Pike worked),[87] Go does not provide any built-in notion of safe or verifiable concurrency. [88] While the communicating-processes model is favored in Go, it is not the only one: all goroutines in a program share a single address space. This means that mutable objects and pointers can be shared between goroutines; see § Lack of race condition safety, below. Although Go's concurrency features are not aimed primarily at parallel processing, [79] they can be used to program shared-memory multi-processor machines. Various studies have been done into the effectiveness of this approach.[89] One of these studies compared the size (in lines of code) and speed of programs written by a seasoned programmer not familiar with the language and corrections to these programs by a Go expert (from Google's development team), doing the same for Chapel, Cilk and Intel TBB. The study found that the non-expert tended to write divide-and-conquer algorithms with one go statement per recursion, while the expert wrote distribute-work-synchronize programs using one goroutine per processor. The expert's programs were usually faster, but also longer. [90] Suitability for parallel programming There are no restrictions on how goroutines access shared data, making race conditions possible. Specifically, unless a program explicitly synchronizes via channels or other means, writes from one goroutine might be partly, entirely, or not at all visible to another, often with no guarantees about ordering of writes.[88] Furthermore, Go's internal data structures like interface values, slice headers, hash tables, and string headers are not immune to race conditions, so type and memory safety can be violated in multithreaded programs that modify shared instances of those types without synchronization.[91][92] Instead of language support, safe concurrent programming thus relies on conventions; for example, Chisnall recommends an idiom called "aliases xor mutable", meaning that passing a mutable value (or pointer) over a channel signals a transfer of ownership over the value to its receiver.

The linker in the gc toolchain creates statically linked binaries by default, therefore all Go binaries include the Go runtime.[93][94] Go deliberately omits certain features common in other languages, including (implementation) inheritance, generic programming, assertions, [e] pointer arithmetic, [d] implicit type conversions, untagged unions, [f] and tagged unions. [g] The designers added only those facilities that all three agreed on.[97] Of the omitted language features, the designers explicitly argue against assertions and pointer arithmetic, while defending the choice to omit type inheritance as giving a more useful language, encouraging instead the use of interfaces to achieve dynamic dispatch[h] and composition to reuse code. Composition and delegation are in fact largely automated by struct embedding; according to researchers Schmager et al., this feature "has many of the drawbacks of inheritance: it affects the public interface of objects, it is not finegrained (i.e, no method-level control over embedding), methods of embedded objects cannot be hidden, and it is static", making it "not obvious" whether programmers will overuse it to the extent that programmers in other languages are reputed to overuse inheritance.[63] The designers express an openness to generic programming and note that built-in functions are in fact typegeneric, but these are treated as special cases; Pike calls this a weakness that may at some point be changed.[55] The Google team built at least one compiler for an experimental Go dialect with generics, but did not release it.[98] They are also open to standardizing ways to apply code generation.[99] Initially omitted, the exception-like panic/recover mechanism was eventually added, which the Go authors advise using for unrecoverable errors such as those that should halt an entire program or server request, or as a shortcut to propagate errors up the stack within a package (but not across package boundaries; there, error returns are the standard API).[100][101][102][103] The Go authors put substantial effort into influencing the style of Go programs: Indentation, spacing, and other surface-level details of code are automatically standardized by the gofmt tool. golint does additional style checks automatically. Tools and libraries distributed with Go suggest standard approaches to things like API documentation (godoc),[104] testing (go test), building (go build), package management Lack of race condition safety Binaries Omissions Style (go get), and so on. Go enforces rules that are recommendations in other languages, for example banning cyclic dependencies, unused variables or imports, and implicit type conversions. The omission of certain features (for example, functional-programming shortcuts like map and Java-style try/finally blocks) tends to encourage a particular explicit, concrete, and imperative programming style. On day one the Go team published a collection of Go idioms,[104] and later also collected code review comments,[105] talks,[106] and official blog posts[107] to teach Go style and coding philosophy. The main Go distribution includes tools for building, testing, and analyzing code: go build, which builds Go binaries using only information in the source files themselves, no separate makefiles go test, for unit testing and microbenchmarks go fmt, for formatting code go get, for retrieving and installing remote packages go vet, a static analyzer looking for potential errors in code go run, a shortcut for building and executing code godoc, for displaying documentation or serving it via HTTP gorename, for renaming variables, functions, and so on in a type-safe way go generate, a standard way to invoke code generators It also includes profiling and debugging support, runtime instrumentation (for example, to track garbage collection pauses), and a race condition tester. An ecosystem of third-party tools adds to the standard distribution, such as gocode, which enables code autocompletion in many text editors, goimports (by a Go team member), which automatically adds/removes package imports as needed, and errcheck, which detects code that might unintentionally ignore errors. package main import "fmt" func main() { fmt.Println("Hello, world!") } where "fmt" is the package for formatted I/O, similar to C's C file input/output. [108] Tools Examples Hello world Concurrency The following simple program demonstrates Go's concurrency features to implement an asynchronous program. It launches two lightweight threads ("goroutines"): one waits for the user to type some text, while the other implements a timeout. The select statement waits for either of these goroutines to send a message to the main routine, and acts on the first message to arrive (example adapted from David Chisnall book).80:152 package main import ( "fmt" "time" ) func readword(ch chan string) { fmt.Println("Type a word, then hit Enter.") var word string fmt.Scanf("%s", &word) ch <- word } func timeout(t chan bool) { time.Sleep(5 time.Second) t <- false } func main() { t := make(chan bool) go timeout(t) ch := make(chan string) go readword(ch) select { case word := <-ch: fmt.Println("Received", word) case <-t: fmt.Println("Timeout.") } } Target function example: func ExtractUsername(email string) string { at := strings.Index(email, "@") return email[:at] } Test code (note that assert keyword is missing in Go; tests live in _test.go at the same package): import ( "testing" ) func TestExtractUsername(t testing.T) { t.Run("withoutDot", func(t testing.T) { username := ExtractUsername("r@google.com") if username != "r" { t.Fatalf("Got: %v\n", username) } }) t.Run("withDot", func(t testing.T) { username := ExtractUsername("jonh.smith@example.com") if username != "jonh.smith" { t.Fatalf("Got: %v\n", username) } }) Testing (https://golang.org/pkg/testing/) } Test run by go test command. How looks like example of running go test -cover -v: === RUN TestIsAvailable === RUN TestIsAvailable/match === RUN TestIsAvailable/notMatch === RUN TestIsAvailable/notMatchBecauseOfStatus === RUN TestIsAvailable/matchWithStatus === RUN TestIsAvailable/matchWithShared === RUN TestIsAvailable/notMatchWithSharedButWrongStatus --- PASS: TestIsAvailable (0.00s) --- PASS: TestIsAvailable/match (0.00s) --- PASS: TestIsAvailable/notMatch (0.00s) --- PASS: TestIsAvailable/notMatchBecauseOfStatus (0.00s) --- PASS: TestIsAvailable/matchWithStatus (0.00s) --- PASS: TestIsAvailable/matchWithShared (0.00s) --- PASS: TestIsAvailable/notMatchWithSharedButWrongStatus (0.00s) === RUN TestIsAccessMatch === RUN TestIsAccessMatch/skMatch === RUN TestIsAccessMatch/skMatch#01 === RUN TestIsAccessMatch/skNotMatch === RUN TestIsAccessMatch/skNotMatch#01 === RUN TestIsAccessMatch/skNotMatch#02 === RUN TestIsAccessMatch/skNotMatchWithAttributes === RUN TestIsAccessMatch/skMatchWithAttributes === RUN TestIsAccessMatch/skMatchWithAttributes#01 --- PASS: TestIsAccessMatch (0.00s) --- PASS: TestIsAccessMatch/skMatch (0.00s) --- PASS: TestIsAccessMatch/skMatch#01 (0.00s) --- PASS: TestIsAccessMatch/skNotMatch (0.00s) --- PASS: TestIsAccessMatch/skNotMatch#01 (0.00s) --- PASS: TestIsAccessMatch/skNotMatch#02 (0.00s) --- PASS: TestIsAccessMatch/skNotMatchWithAttributes (0.00s) --- PASS: TestIsAccessMatch/skMatchWithAttributes (0.00s) --- PASS: TestIsAccessMatch/skMatchWithAttributes#01 (0.00s) === RUN TestIsStatusMatch === RUN TestIsStatusMatch/emptyToInProgress === RUN TestIsStatusMatch/emptyToComplete === RUN TestIsStatusMatch/emptyToArchive === RUN TestIsStatusMatch/archived --- PASS: TestIsStatusMatch (0.00s) --- PASS: TestIsStatusMatch/emptyToInProgress (0.00s) --- PASS: TestIsStatusMatch/emptyToComplete (0.00s) --- PASS: TestIsStatusMatch/emptyToArchive (0.00s) --- PASS: TestIsStatusMatch/archived (0.00s) === RUN TestGetEmail --- PASS: TestGetEmail (0.00s) === RUN TestGetProjectName --- PASS: TestGetProjectName (0.00s) === RUN TestGetUserName --- PASS: TestGetUserName (0.77s) PASS coverage: 55.0% of statements ok _/home/username/projectName 0.784s It is possible to run tests in parallel. Vim 8 on Linux with Syntastic plugin that reports error in Go code Popular tools for working with Go code: GoLand[109] : an IDE by JetBrains Visual Studio Code: free popular extensible text editor on Electron LiteIDE: a "simple, open source, cross-platform Go IDE",[110] Vim: also user can install plugins: vim-go (https://github.com/fatih/vim-go) ALE (https://github.com/dense-analysis/ale): asynchronous linter for many languages, but currently with known issue (https://github.com/dense-analysis/ale/issues/ 2517) Syntastic (https://github.com/vim-syntastic/syntastic): also linter, for many languages, but wait for linter on save Some notable open-source applications written in Go include:[111] Caddy, an open source HTTP/2 web server with automatic HTTPS capability. CockroachDB, an open source, survivable, strongly consistent, scale-out SQL database. Docker, a set of tools for deploying Linux containers Ethereum, The go-ethereum implementation of the Ethereum Virtual Machine blockchain for the Ether cryptocurrency [112] Hugo, a static site generator InfluxDB, an open source database specifically to handle time series data with high availability and high performance requirements. InterPlanetary File System, a content-addressable, peer-to-peer hypermedia protocol.[113] Juju, a service orchestration tool by Canonical, packagers of Ubuntu Linux Kubernetes container management system lnd, an implementation of the Bitcoin Lightning Network. [114] Mattermost, a teamchat system NATS Messaging, is an open-source messaging system featuring the core design principles of performance, scalability, and ease of use.[115] OpenShift, a cloud computing platform as a service by Red Hat Snappy, a package manager for Ubuntu Touch developed by Canonical. Syncthing, an open-source file synchronization client/server application Terraform, an open-source, multiple cloud infrastructure provisioning tool from HashiCorp. Other notable companies and sites using Go (generally together with other languages, not exclusively) include: Cacoo, for their rendering of the user dashboard page and microservice using Go and gRPC.[116] Editing environments Applications Chango, a programmatic advertising company uses Go in its real-time bidding systems.[117] Cloud Foundry, a platform as a service[118] Cloudflare, for their delta-coding proxy Railgun, their distributed DNS service, as well as tools for cryptography, logging, stream processing, and accessing SPDY sites.[119][120] Container Linux (formerly CoreOS), a Linux-based operating system that uses Docker containers[121] and rkt containers. Couchbase, Query and Indexing services within the Couchbase Server[122] Dropbox, who migrated some of their critical components from Python to Go[123] Google, for many projects, notably including download server dl.google.com[124][125][126] Heroku, for Doozer, a lock service[15] Hyperledger Fabric, an open source, enterprise-focused distributed ledger project MongoDB, tools for administering MongoDB instances[127] Netflix, for two portions of their server architecture[128] Nutanix, for a variety of micro-services in its Enterprise Cloud OS.[129] Plug.dj, an interactive online social music streaming website.[130] SendGrid, a Boulder, Colorado-based transactional email delivery and management service.[131] SoundCloud, for "dozens of systems"[132] Splice, for the entire backend (API and parsers) of their online music collaboration platform.[133] ThoughtWorks, some tools and applications for continuous delivery and instant messages (CoyIM).[134] Twitch, for their IRC-based chat system (migrated from Python).[135] Uber, for handling high volumes of geofence-based queries.[136] The interface system, and the deliberate omission of inheritance, were praised by Michele Simionato, who likened these characteristics to those of Standard ML, calling it "a shame that no popular language has followed [this] particular route".[137] Dave Astels at Engine Yard wrote:[138] Go is extremely easy to dive into. There are a minimal number of fundamental language concepts and the syntax is clean and designed to be clear and unambiguous. Go is still experimental and still a little rough around the edges. Go was named Programming Language of the Year by the TIOBE Programming Community Index in its first year, 2009, for having a larger 12-month increase in popularity (in only 2 months, after its introduction in November) than any other language that year, and reached 13th place by January 2010,[139] surpassing established languages like Pascal. By June 2015, its ranking had dropped to below 50th in the index, placing it lower than COBOL and Fortran. [140] But as of January 2017, its ranking had surged to 13th, indicating significant growth in popularity and adoption. Go was awarded TIOBE programming language of the year 2016. Bruce Eckel has stated:[141] Reception The complexity of C++ (even more complexity has been added in the new C++), and the resulting impact on productivity, is no longer justified. All the hoops that the C++ programmer had to jump through in order to use a C-compatible language make no sense anymore -- they're just a waste of time and effort. Go makes much more sense for the class of problems that C++ was originally intended to solve. A 2011 evaluation of the language and its gc implementation in comparison to C++ (GCC), Java and Scala by a Google engineer found: Go offers interesting language features, which also allow for a concise and standardized notation. The compilers for this language are still immature, which reflects in both performance and binary sizes. — R. Hundt[142] The evaluation got a rebuttal from the Go development team. Ian Lance Taylor, who had improved the Go code for Hundt's paper, had not been aware of the intention to publish his code, and says that his version was "never intended to be an example of idiomatic or efficient Go"; Russ Cox then optimized the Go code, as well as the C++ code, and got the Go code to run slightly faster than C++ and more than an order of magnitude faster than the code in the paper. [143] On November 10, 2009, the day of the general release of the language, Francis McCabe, developer of the Go! programming language (note the exclamation point), requested a name change of Google's language to prevent confusion with his language, which he had spent 10 years developing.[144] McCabe raised concerns that "the 'big guy' will end up steam-rollering over" him, and this concern resonated with the more than 120 developers who commented on Google's official issues thread saying they should change the name, with some[145] even saying the issue contradicts Google's motto of: Don't be evil. [146] On October 12, 2010, the issue was closed by Google developer Russ Cox (@rsc) with the custom status "Unfortunate" accompanied by the following comment: "There are many computing products and services named Go. In the 11 months since our release, there has been minimal confusion of the two languages."[146] Go critics assert that: The lack of parametric polymorphism for generic programming leads to code duplication or unsafe type conversions and flow disrupting verbosity. [147][148][149][150] Go's nil combined with the lack of algebraic types leads to difficulty handling failures and base cases. [147][149] Go does not allow an opening brace to appear on its own line, which forces all Go programmers to use the same brace style.[151] Naming dispute Criticism C (programming language) Comparison of programming languages a. But "To allow complex statements to occupy a single line, a semicolon may be omitted before a closing ) or }".[51] b. “if the newline comes after a token that could end a statement, [the lexer will] insert a semicolon”.[52] c. Usually, exactly one of the result and error values has a value other than the type's zero value; sometimes both do, as when a read or write can only be partially completed, and sometimes neither, as when a read returns 0 bytes. See Semipredicate problem: Multivalued return. d. Language FAQ "Why is there no pointer arithmetic? Safety … never derive an illegal address that succeeds incorrectly … using array indices can be as efficient as … pointer arithmetic … simplify the implementation of the garbage collector…."[12] e. Language FAQ "Why does Go not have assertions? …our experience has been that programmers use them as a crutch to avoid thinking about proper error handling and reporting…."[12] f. Language FAQ "Why are there no untagged unions…? [they] would violate Go's memory safety guarantees."[12] g. Language FAQ "Why does Go not have variant types? … We considered [them but] they overlap in confusing ways with interfaces…. [S]ome of what variant types address is already covered, … although not as elegantly."[12] (The tag of an interface type[95] is accessed with a type assertion[96] ). h. Questions "How do I get dynamic dispatch of methods?" and "Why is there no type inheritance?" in the language FAQ.[12]

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