!!! BREAKING CHANGE !!! - remove the custom implementation of std::is_constructible and optionally use the <type_traits> header because of infinite template recursion issues with GCC

[chambm]

Description

Template depth exceeded on GCC

Here is a repro:
http://coliru.stacked-crooked.com/a/be9f09a38e109b69

I pasted current doctest.h in there and tacked a test case at the end.

I found the bug working with GCC 4.8.4, so it's not the GCC version. What is that template metaprogramming for in the Approx class? Seems a bit overly complex.

Extra information

• doctest version: 1.2.1
• Compiler+version: GCC 7.1.0

[onqtam]

interestingly enough clang has no trouble but all versions of GCC fail...

I originally added the is_constructible type trait to support strong typedefs of double for doctest::Approx - and took the implementation from here (and "simplified" it) because using std::is_constructible would require including <type_traits>...

I'm not sure how to proceed with this - it might be a gcc problem, but it is for sure a huge template mess...

sometimes I look back at things I've added and say to myself "what was I thinking"...

[chambm]

It also works on MSVC 12 and later. At least Update 5. I've seen an internal compiler error with VC 12 update 1 but couldn't figure out how to reproduce it. Been wondering whether it was related to this.

[onqtam]

I'll probably address this next week by making a config option (another one... off by default) to support strong typedefs of double for Approx which would trigger including <type_traits> and the use of std::is_constructible - a breaking change for users currently using that...

[chambm]

A good compromise!

[onqtam]

this is now in the dev branch - soon I'll release version 1.2.2 with this going into master.