Fix build for C++20, Fix #53

[andreasWallner]

As reported in #53:

C++20 removed the deprecated std::result_of in favor of std::invoke_result. Switch between usage of those depending on the cpp_lib_is_invocable feature test macro.

See:

• https://en.cppreference.com/w/cpp/types/result_of
• https://en.cppreference.com/w/cpp/feature_test#Library_features

An alternative solution would be to use decltype instead of either of those two templates, if you prefer that I'd be happy to update my PR.

[nicola-gigante]

Hi, I need this P.R. merged to use clipp in a C++20 project. What is blocking merging it?

[Pospelove]

please consider merging this pr

[DominikGrabiec]

If you use vcpkg then this patch is being applied care of https://github.com/microsoft/vcpkg/issues/27167

[danyhm]

If you use vcpkg then this patch is being applied care of microsoft/vcpkg#27167

the patch still doesn't fix the compilation. i still get this error with c++20

Severity	Code	Description	Project	File	Line	Suppression State
Warning	C26495	Variable 'clipp::group::child_t<clipp::parameter,clipp::group>::data::group' is uninitialized. Always initialize a member variable (type.6).		C:\dev\vcpkg\installed\x86-windows-static\include\clipp.h	2772	
Error (active)	E0312	no suitable user-defined conversion from "const clipp::group::child" to "const clipp::group::child" exists	C:\dev\vcpkg\installed\x86-windows-static\include\clipp.h	2968	
Error (active)	E0120	return value type does not match the function type	C:\dev\vcpkg\installed\x86-windows-static\include\clipp.h	2973	
Error (active)	E0040	expected an identifier	C:\dev\vcpkg\installed\x86-windows-static\include\clipp.h	6324	
Error (active)	E0040	expected an identifier	C:\dev\vcpkg\installed\x86-windows-static\include\clipp.h	6734	
Error (active)	E0070	incomplete type is not allowed	C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\VC\Tools\MSVC\14.29.30133\include\type_traits	762	
Error (active)	E0852	expression must be a pointer to a complete object type	C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\VC\Tools\MSVC\14.29.30133\include\vector	1752	
Error (active)	E0393	pointer to incomplete class type "_MAC_adapter_raw_info" is not allowed	C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\VC\Tools\MSVC\14.29.30133\include\xmemory	311	
Error (active)	E0070	incomplete type is not allowed	C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\VC\Tools\MSVC\14.29.30133\include\xmemory	797	
Error (active)	E0852	expression must be a pointer to a complete object type	C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\VC\Tools\MSVC\14.29.30133\include\xmemory	904	
Warning	C26495	Variable 'clipp::group::child_t<clipp::parameter,clipp::group>::data::param' is uninitialized. Always initialize a member variable (type.6).	C:\dev\vcpkg\installed\x86-windows-static\include\clipp.h	2772	
Warning	C26495	Variable 'clipp::group::depth_first_traverser::memento::level_' is uninitialized. Always initialize a member variable (type.6).	C:\dev\vcpkg\installed\x86-windows-static\include\clipp.h	2831	
Warning	C4003	not enough arguments for function-like macro invocation 'max'	C:\dev\vcpkg\installed\x86-windows-static\include\clipp.h	332	
Warning	C4003	not enough arguments for function-like macro invocation 'max'	C:\dev\vcpkg\installed\x86-windows-static\include\clipp.h	333	
Error	C2589	'(': illegal token on right side of '::'	C:\dev\vcpkg\installed\x86-windows-static\include\clipp.h	332	
Error	C2589	'(': illegal token on right side of '::'	C:\dev\vcpkg\installed\x86-windows-static\include\clipp.h	5909	
Error	C2589	'(': illegal token on right side of '::'	C:\dev\vcpkg\installed\x86-windows-static\include\clipp.h	6324	
Error	C2062	type 'unknown-type' unexpected	C:\dev\vcpkg\installed\x86-windows-static\include\clipp.h	6324	
Error	C2059	syntax error: ')'	C:\dev\vcpkg\installed\x86-windows-static\include\clipp.h	6324	
Error	C2589	'(': illegal token on right side of '::'	C:\dev\vcpkg\installed\x86-windows-static\include\clipp.h	6734	
Error	C2062	type 'unknown-type' unexpected	C:\dev\vcpkg\installed\x86-windows-static\include\clipp.h	6734	
Error	C2059	syntax error: ')'	C:\dev\vcpkg\installed\x86-windows-static\include\clipp.h	6734	

[DominikGrabiec]

@danyhm That's a different error that you have.

Maybe you can try https://github.com/GerHobbelt/clipp as that seems to be more up to date.