MSVC2017, 15.5 new issues.

[aj664]

yesterday 2017.12.05 using MSVC2017, 15.4.4 was compiling v.2.1.1 fine.
today, upgraded to MSVC2017 15.5.. now v2.1.1 has lots of std::allocator warnings/errors.

[nlohmann]

Related: #856

[aj664]

if you aren't going to make the changes MS suggest for reasons of other-compiler compatibility, then at least add the #define the error suggests to suppress the warning.

[nlohmann]

What is Microsoft suggesting? I am not using MSVC myself, so I am surprised that existing code would break with a new MSVC version.

[aj664]

#define _SILENCE_CXX17_OLD_ALLOCATOR_MEMBERS_DEPRECATION_WARNING

if you wanted to add #if _MSC_VER >= 1912 around that too, it might help readers to understand when/if/what it's for.

[nlohmann]

Is this relevant unless you choose C++17 as standard? Did you try whether the code of #856 still exhibits these warnings?

[aj664]

I am compiling with C++17, i imagine a lot of people now do. after adding
#define _SILENCE_CXX17_OLD_ALLOCATOR_MEMBERS_DEPRECATION_WARNING
all warnings/errors have gone; and v.2.1.1 compiles without error again.

i don't see a reason not to add this #define, it's clearly something that will need to be addressed eventually. it breaks builds without it. it's a C++17 issue, not a MS specific one, it's just co-incidence the first compiler to deprecate it is the MS one. By adding this define i don't think you are hiding a bug, just a valid deprecation warning.

[nlohmann]

If I understand correctly, #856 is addressing these warnings by solving them instead of defining away the deprecation warnings.

[aj664]

I think it is attempting that, but if that fails to work because it's introducing features only supported in C++17 then that would break your C++11 support?! Aren't you trying to support C++11 still? are the proposed std::allocator_traits a supported C++11 feature?!

if the patch can not be applied because of breaking changes, then the #define _SILENCE_CXX17_OLD_ALLOC.. would allow the old code to continue to work, AND allow modern compilation to succeed.

[nlohmann]

Seems like it's a C++11 feature: http://en.cppreference.com/w/cpp/memory/allocator_traits

[nlohmann]

@aj664 Could you check whether #856 fixes the warnings? Alternatively, could you post the error/warning messages you mentioned in your report?

[nlohmann]

(#856 is merged, so could someone check the develop branch with MSVC2017?)

[erengy]

I can confirm that #856 fixes the following warning in Visual Studio 2017 version 15.5:

warning STL4010: Various members of std::allocator are deprecated in C++17. Use std::allocator_traits instead of accessing these members directly. You can define _SILENCE_CXX17_OLD_ALLOCATOR_MEMBERS_DEPRECATION_WARNING or _SILENCE_ALL_CXX17_DEPRECATION_WARNINGS to acknowledge that you have received this warning.

I get a couple of these with v2.1.1, but the develop branch is fine.