Error: Compiling with MSVC

[abeimler]

Hello, I have some problems compiling fixed-containers on Windows, after updating the library in my project. (from 7725f0141aecddcf26118f059d952050bda73383 (Jun. 2021) to the newses 62e81fb596116485247d653b779501ed10a97843 (Oct. 2021)) I only use FixedVector, EnumMap and EnumSet

Now I get this Error:

Error   C7599   'fixed_containers::IteratorConstness::IteratorConstness': a trailing requires clause is only allowed on a templated fixed_containers\iterator_utils.hpp 16  
Error   C2891   'CONSTNESS': cannot take the address of a template parameter    fixed_containers\bidirectional_iterator.hpp 29  

So I pulled this project with all the tests, try to build it and got the same errors.

Steps to Reproduce:

1. git clone https://github.com/teslamotors/fixed-containers
2. cd fixed-containers
3. Install dependencies:

                git submodule add https://github.com/Microsoft/vcpkg.git vcpkg
                ./vcpkg/bootstrap-vcpkg.bat
                ./vcpkg/vcpkg install magic-enum ms-gsl range-v3 gtest

4. Configure and Build:

                 mkdir build
                 cmake -S . -B build -DCMAKE_TOOLCHAIN_FILE=./vcpkg/scripts/buildsystems/vcpkg.cmake
                 cmake --build build

   Had to modify the dependencies in the CMakeList.txt for vcpkg to work:

find_package(magic_enum CONFIG REQUIRED)

find_package(Microsoft.GSL CONFIG REQUIRED)

find_package(range-v3 CONFIG REQUIRED)

find_package(GTest CONFIG REQUIRED)

macro(add_test_dependencies TEST_TARGET) target_link_libraries(${TEST_TARGET} PRIVATE magic_enum::magic_enum) target_link_libraries(${TEST_TARGET} PRIVATE GTest::gtest GTest::gtest_main)

target_link_libraries(${TEST_TARGET} PRIVATE Microsoft.GSL::GSL)

#target_link_libraries(${TEST_TARGET} PRIVATE range-v3 range-v3-meta range-v3::meta range-v3-concepts)

target_include_directories(${TEST_TARGET} PRIVATE include)
add_test(NAME ${TEST_TARGET} COMMAND ${TEST_TARGET})

endmacro()

### Environment:

 * **OS:** Windows 10
 * **Compiler:** MSVC 19.29.30136.0
 * **IDE:** Visual Studio 2019

## Error

**Compiler-Error:**
```bash
Error   C7599   'fixed_containers::IteratorConstness::IteratorConstness': a trailing requires clause is only allowed on a templated function    fixed-containers\include\fixed_containers\iterator_utils.hpp    16  
Error   C7599   'fixed_containers::IteratorDirection::IteratorDirection': a trailing requires clause is only allowed on a templated function    fixed-containers\include\fixed_containers\iterator_utils.hpp    88  
Error   C2891   'CONSTNESS': cannot take the address of a template parameter    fixed-containers\include\fixed_containers\bidirectional_iterator.hpp    29  
Error   C2891   'CONSTNESS': cannot take the address of a template parameter    fixed-containers\include\fixed_containers\bidirectional_iterator.hpp    35  
Error   C2891   'CONSTNESS': cannot take the address of a template parameter    fixed-containers\include\fixed_containers\bidirectional_iterator.hpp    38  
Error   C2891   'CONSTNESS': cannot take the address of a template parameter    fixed-containers\include\fixed_containers\random_access_iterator_transformer.hpp    30  
Error   C2891   'CONSTNESS': cannot take the address of a template parameter    fixed-containers\include\fixed_containers\random_access_iterator_transformer.hpp    37  
Error   C2891   'CONSTNESS': cannot take the address of a template parameter  fixed_containers\random_access_iterator_transformer.hpp   40  
Error   C2891   'CONSTNESS': cannot take the address of a template parameter    fixed-containers\include\fixed_containers\random_access_iterator_transformer.hpp    41  
Error   C7599   'fixed_containers::fixed_red_black_tree_detail::RedBlackTreeNodeColorCompactness::RedBlackTreeNodeColorCompactness': a trailing requires clause is only allowed on a templated function fixed-containers\include\fixed_containers\fixed_red_black_tree_nodes.hpp    20  
Error   C2891   'COMPACTNESS': cannot take the address of a template parameter  fixed-containers\include\fixed_containers\fixed_red_black_tree_nodes.hpp    292 
Error   C2891   'COMPACTNESS': cannot take the address of a template parameter  fixed-containers\include\fixed_containers\fixed_red_black_tree_storage.hpp  59  
....

Side Note:

1. Other Compiler Error I found with MSVC:

   Error   C7595   'fixed_containers::StringLiteral::StringLiteral': call to immediate function is not a constant expression    fixed-containers\include\fixed_containers\string_literal.hpp   38  

Easy fix, just set members in the initializer list:

constexpr StringLiteral() noexcept
  : size_(0)
  , cstr_("")
{
}

2. current fixed-containers works fine with Linux and clang-compiler (compiled my other project in Linux and it works fine)
3. tried to compile with clang on Windows, had some problems running clang on Windows in Visual Studio 2019

[alexkaratarakis]

Thanks for the detailed write-up! I will investigate these issues.

[alexkaratarakis]

This is now fixed. Latest main builds cleanly with msvc and gcc.