Get the size of an std::array as r-value

Question

Consider the following snippet of code:

#include<array>
#include<cstdint>

const std::array<int, 3> array{0, 1 , 2};

template<class string_type>
auto parse(string_type&& name) {
        const auto s = std::uint8_t{array.size()};
        return s;
}

While it compiles using gcc 9.3.0 (the default on Ubuntu 20.04), it fails with gcc 11.2.0 (built from sources) with the following error message:

test2.cpp: In function ‘auto parse(string_type&&)’:
test2.cpp:8:47: error: no matching function for call to ‘std::array<int, 3>::size(const std::array<int, 3>*)’
    8 |         const auto s = std::uint8_t{array.size()};
      |                                     ~~~~~~~~~~^~
In file included from test2.cpp:1:
/opt/modules/install/gcc/11.2.0/include/c++/11.2.0/array:176:7: note: candidate: ‘constexpr std::array<_Tp, _Nm>::size_type std::array<_Tp, _Nm>::size() const [with _Tp = int; long unsigned int _Nm = 3; std::array<_Tp, _Nm>::size_type = long unsigned int]’
  176 |       size() const noexcept { return _Nm; }
      |       ^~~~
/opt/modules/install/gcc/11.2.0/include/c++/11.2.0/array:176:7: note:   candidate expects 0 arguments, 1 provided

Running example

Besides the fact that it does not make much sense, I can't find where is the error, can you help me?

Answer 1

It appears to be a bug in:

• gcc-10: https://godbolt.org/z/95TTv4z9P and
• gcc-11: https://godbolt.org/z/KWMs4MMcK

It works fine in:

• gcc-9: https://godbolt.org/z/YMqsMjr7x and
• clang: https://godbolt.org/z/6Kq9nY7bo

To work around, you can do either this:

const auto s = static_cast<std::uint8_t>(array.size());

or this:

const std::uint8_t s = array.size();

or this (but please don't):

const auto s = std::uint8_t( array.size() );

I would suggest this:

#include<array>
#include<cstdint>

const std::array<int, 3> array{ 0, 1 , 2 };

template<class string_type>
auto parse(string_type&& name)
{
    const std::uint8_t s = array.size();
    return s;
}

Running example