thread_local is not supported on iOS 9.0

[theodelrieu]

Description

thread_local is not supported on iOS 9.0.

Steps to reproduce

• Use doctest and target iOS 9.0

Extra information

• doctest version: v2.0.1
• Operating System: iOS 9.0
• Compiler+version: AppleClang 10.0

[theodelrieu]

I'm afraid this one will be a bit harder to fix than #163 ...

[onqtam]

On the top of my head - version 1.2.8 doesn't use anything thread-local and is C++98 - there is also a git tag... for now that is the best I can offer. The interface (API) is the same.

I suppose iOS 9 will be out of support soon...?

[theodelrieu]

Fair enough, I don't really need to build tests on iOS anyway, if I do, I'll go back to 1.2.8.

Thanks!

[lasagnaphil]

Although the issue is closed as of right now, I'd like to share how I solved this problem. Right now, I'm building with MinGW clang (on Windows), which has some issues with thread_local. Fortunately, using a custom implementation of thread_local (https://github.com/wang-bin/ThreadLocal) solved the issue, although I had to edit a few lines of code in doctest.h.

Maybe in a later release, we could add the custom implementation for platforms not supporting thread_local (such as MinGW clang, vs2013, and some versions of iOS/Android).

[onqtam]

@lasagnaphil I actually made it possible to use the latest doctest version 2.2.1 with platforms not supporting thread_local - see this issue:

#172

All you have to do is just to define DOCTEST_THREAD_LOCAL before including the header (without a value - just have it defined) - but don't use doctest in a multi-threaded context :)