CODEWITHSUNDEEP
c++g++c++-concepts
Tristan Brindle
Tristan Brindle

Reputation: 16824

Detecting the Concepts TS with GCC 6.1

How can I detect the presence of the Concepts TS with GCC 6.1?

This page suggests that the macro __cpp_experimental_concepts should be predefined in a Concepts TS-supporting implementation. However, the following test program compiles without error on GCC 6.1 with the -fconcepts flag:

#ifdef __cpp_experimental_concepts
static_assert(false, "Concepts TS found");
#endif

template <typename T>
concept bool Identity = true;

int main() {}

(I would expect either the static_assert to fire, or the concept keyword to go unrecognised.)

Does anyone know of any other method to conditionally compile code based on whether Concepts are available?

Upvotes: 2

Views: 556

Answers (1)

Holt
Holt

Reputation: 37626

The correct macro is __cpp_concepts for GCC:

#ifdef __cpp_concepts
static_assert(false, "Concepts TS found");
#endif

According to this, the name of the macro was changed in a recent draft.

The correct name is from the GCC support page (thanks to Jonathan Wakely), but the linked draft (2015-02-09) still requires __cpp_experimental_concepts (which is strange... ). However, in this more recent draft (2015-09-25), the name has actually been changed to __cpp_concepts.

Upvotes: 5

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