String formatting and print(f)

[dnsmichi]

Describe the solution you'd like

User-friendly support for formatting strings based on specific format patterns. Independent from the value type, printf style, or Python style - common to the users.

A Printing class as entry point for:

• DSL script functions: print, printf
• Internal utility functions, e.g. Utility::Format()
• Logging (structured logging, etc.)

Creating a custom solution is a no-go, we'll need to evaluate possible candidates out there. Header only includes are preferred.

Related Issues

• Some kind of print() statement for API Console #6764
• printf-style formatting for String type #4712

Describe alternatives you've considered

https://github.com/fmtlib/fmt will be the base for C++ 20's std::format implementation. Therefore it is safe to assume we can be use it and later convert to the standard library if needed.

http://www.zverovich.net/2019/07/23/std-format-cpp20.html

If we consider replacing our logging library, spdlog also uses fmt under the hood. https://github.com/gabime/spdlog

Benchmarks

• fmt: https://github.com/fmtlib/fmt#benchmarks

[dnsmichi]

@htriem Please evaluate the library fmt during the coming weeks, when you got time.

• [ ] Collect a list of examples how to implement this library, create them and add them to a presentation
• [ ] Create benchmarks comparing fmt to ostringstream and boost::format
• [ ] Document how this library can be integrated into CMake

Once done, continue with the integration into Icinga 2:

• [ ] Create a CMake integration skeleton (find script, header only library) for Icinga 2 - feature branch
• [ ] Implement printf for the String class and show how it works in the DSL - feature branch
• [ ] Alternate implementions, e.g. global script function. Weigh them.

Logging

• [ ] Implement/change some of the logging functions in Icinga and use fmt for them instead of the shift operator
• [ ] Prepare ideas for spdlog and logging libraries (https://www.youtube.com/watch?v=xzu245IqDbA&list=PLeoxx10paaAmYXoGv54pfTbLHCZYMSN34&index=12&t=6s)

[dnsmichi]

Header only: https://github.com/fmtlib/fmt/issues/596#issuecomment-341617817

#define FMT_HEADER_ONLY
#include "fmt/format.h"

[htriem]

Looks like this is more complicated to implement inside the DSL. We need to find a way to map a list of array items from fmt to the Icinga DSL. Therefore TBD.

[julianbrost]

Is there a real need for this? Sure, would be nice to have but this has been lying around for some time with no progress, so maybe wontfix for the foreseeable future?

[Al2Klimov]

@htriem You're not working on this, right?

[htriem]

Not currently, no.