Assignment broken with msvc once again

[lukester1975]

Accidental (?) reversion of the fix from #21 by the looks of it in 875c5de:

(void(B1::value = static_cast<U&&>(u).B2::value), ...);
was changed back to:
(void(B1::value = static_cast<U&&>(u).identity_t<B2>::value), ...);

Remove identity_t and all is well again, but maybe a better fix is needed if that identity_t is really there for a reason!

Also it appears to manifest only in c++20 mode. At least the tests all compile and work by default, but that seems to be in c++17 mode. Trying to configure cmake with -DCXX_STANDARD=20 caused all sorts of std::format weirdness. I don't really have the time to look in to that; I'm just going to apply the old fix locally as it was working fine but here's a simple test instead:

#include <cassert>
#include <tuplet/tuple.hpp>

int main()
{
	int a = -1;
	tuplet::tie(a) = tuplet::make_tuple(123);
	assert(a == 123);
}

With c++20:

 cl test.cpp /std:c++20 -I./include && ./test.exe
Microsoft (R) C/C++ Optimizing Compiler Version 19.34.31937 for x64
Copyright (C) Microsoft Corporation.  All rights reserved.

test.cpp
Microsoft (R) Incremental Linker Version 14.34.31937.0
Copyright (C) Microsoft Corporation.  All rights reserved.

/out:test.exe
test.obj
Assertion failed: a == 123, file test.cpp, line 8

And 17:

 cl test.cpp /std:c++17 -I./include && ./test.exe
Microsoft (R) C/C++ Optimizing Compiler Version 19.34.31937 for x64
Copyright (C) Microsoft Corporation.  All rights reserved.

test.cpp
Microsoft (R) Incremental Linker Version 14.34.31937.0
Copyright (C) Microsoft Corporation.  All rights reserved.

/out:test.exe
test.obj

Sadly no movement at all in https://developercommunity.visualstudio.com/t/fold-expressions-unreliable-in-171-with-c20/1676476

Thanks!

[lukester1975]

Had another look. I guess it was reverted because the old fix actually broke the new c++17 support!

Here's a different version, all green (it's one of the other approaches from my initial investigation): https://github.com/lukester1975/tuplet/tree/fix-cl-again

Thanks