CODEWITHSUNDEEP
c++enable-if
Pascal T.
Pascal T.

Reputation: 4081

how to std::variant<unsigned long, size_t, unsigned int>

I ran into a portability issue, which is due to the fact that size_t varies between platforms (sometimes it is equiv to unsigned int, sometimes to unsigned long)

What I would like to write is:


"if constexpr" / "enable_if" / "whatever"  (size_t == unsigned long)
  using V = std::variant<unsigned int, size_t>;
else
  using V = std::variant<unsigned long, size_t>;

What is the less ugly way to write it?

Links to compiler explorer snippet:

https://godbolt.org/z/AZVFEz : using gcc 9.2 64 bits where size_t <-> unsigned long

https://godbolt.org/z/wWeCbW : using msvc 19.22 32 bits where size_t <-> unsigned int

Upvotes: 3

Views: 335

Answers (1)

StoryTeller - Unslander Monica
StoryTeller - Unslander Monica

Reputation: 170104

Since you want a conditional type alias, you may use std::conditional

using V = std::conditional_t<std::is_same_v<std::size_t, unsigned long>,
            std::variant<unsigned int, size_t>,
            std::variant<unsigned long, size_t>
          >;

Upvotes: 2

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