Formatting of non-const-formattable types about value_types

[jbcoe]

We need to look at other standard library types and do the same thing. No need to innovate here.

[Twon]

Perhaps I'm missing something but I can't get this example working for the use case. Currently, only the latest Visual Studio has support for the <print> header, any ideas what I am missing to reproduce this: https://godbolt.org/z/ahWacdanP

[Ukilele]

Here is the original sample: https://godbolt.org/z/zh9czreoK

Here is a "simplified" version which does not involve ranges, but my own custom type that is only formattable in a non-const verison (MyNonConstFormattableType) https://godbolt.org/z/sqoE5Txfj

It seems that both only work with clang 17.0.1 and options: -std=c++23 -stdlib=libc++

[Ukilele]

Regarding a solution: I just checked https://eel.is/c++draft/format.tuple#lib:format,formatter . This is the std::formatter for std::pair and std::tuple. The approach seems to be: If const T is formattable, then format takes a const std::tuple<T>& as parameter, otherwise it takes a std::tuple<T>& as parameter. Something similar was done at https://eel.is/c++draft/format.range, too.

[Ukilele]

I just learned, that libc++ does not define the macro __cpp_lib_format yet. This gets used in https://github.com/jbcoe/value_types/blob/main/indirect.h#L348 . So therefore under libc++ (which all my godbolt-samples used), the code will never work, because the #ifdef (#if (__cpp_lib_format >= 201907L)) in indirect.h will always be false.

[jbcoe]

Feel free to add your experiment in a PR and piggy-back off our test setup. We run on MSVC, Clang and GCC.

[jbcoe]

We've stripped out format support altogether so this is no longer an issue.