Namespaces
Variants

    std::meta::extent

    From cppreference.com
    < cpp | meta
     
    C++
     
    Metaprogramming library
     
    Reflection library
     
    Reflection types and queries
        
    Type properties
    Type property queries
     
    Defined in header <meta> 
    consteval std::size_t extent( std::meta::info r, unsigned i = 0 );
    		(since C++26)

    If r represents an array type, returns the number of elements along the ith dimension of the array, if i is in range [0, std::meta::rank(^^r)). For any other type, or if r represents an array of unknown bound along its first dimension and i is 0, returns 0.

    Equivalent to std::extent<T, I>::value, where T is the type represented by std::meta::dealias(r) and I is a constant equal to i.

    Parameters

    r - a reflection value

    Return value

    The number of elements along the specified dimension i, if r represents an array type and i is within the rank range. Otherwise 0.

    Exceptions

    std::meta::exception if r does not represent a type or type alias.

    Example

    Run this code
    #include <meta>

static_assert
(""
    && extent(^^int[3]) == 3        // default dimension is 0
    && extent(^^int[3], 0) == 3     // dimension 0 has 3 elements
    && extent(^^int[3], 1) == 0     // dimension index is out of range
    && extent(^^int[3][4], 0) == 3
    && extent(^^int[3][4], 1) == 4
    && extent(^^int[3][4], 2) == 0  // dimension index is out of range
    && extent(^^int[]) == 0
);

int main()
{
    const auto ext = extent(^^int[8]);
    static_assert(ext == 8); // with implicit conversion to std::size_t

    const int ints[]{1, 2, 3, 4};
    static_assert(extent(^^decltype(ints)) == 4); // array size

    [[maybe_unused]] int ary[][3] = { {1, 2, 3} };

    // ary[0] is of type reference to int[3], so, the extent
    // cannot be calculated correctly and it returns 0
    static_assert(std::meta::is_same_type(^^decltype(ary[0]), ^^int(&)[3]));
    static_assert(extent(^^decltype(ary[0])) == 0);

    // removing reference gives correct extent value 3
    static_assert(extent(std::meta::remove_cvref(^^decltype(ary[0]))) == 3);
}

    See also

    (C++26)
    		 checks if reflected type is an array type
    (function) [edit]
    (C++26)
    		 removes one extent from reflected array type
    (function) [edit]
    (C++26)
    		 removes all extents from reflected array type
    (function) [edit]
    (C++26)
    		 obtains the number of dimensions of reflected array type
    (function) [edit]
    (C++23)
    		 a descriptor of a multidimensional index space of some rank
    (class template) [edit]
    (C++11)
    		 obtains the size of an array type along a specified dimension
    (class template) [edit]