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std::ranges::elements_of

Defined in header <ranges> 
template< ranges::range R, class Allocator = std::allocator<std::byte> >
struct elements_of {
    [[no_unique_address]] R range;
    [[no_unique_address]] Allocator allocator = Allocator();
};
 (since C++23)

Encapsulates a range. Specializations of elements_of act as a tag in overload sets to disambiguate when a range should be treated as a sequence rather than a single value.

Deduction guide

template< class R, class Allocator = std::allocator<std::byte> >
elements_of( R&&, Allocator = Allocator() ) -> elements_of<R&&, Allocator>;

Example

#include <any>
#include <generator>
#include <iostream>
#include <ranges>
#include <string_view>
 
template<bool Elementwise>
std::generator<std::any> gen(std::ranges::input_range auto&& r)
{
    if constexpr (Elementwise)
        co_yield std::ranges::elements_of(r); // yield each element of r
    else
        co_yield r;                           // yield r as a single value
}
 
int main()
{
    auto test = std::string_view{"test"};
 
    for (std::any a : gen<true>(test))
        std::cout << '[' << std::any_cast<char>(a) << "] ";
    std::cout << '\n';
 
    for (std::any a : gen<false>(test))
        std::cout << '[' << std::any_cast<std::string_view>(a) << "] ";
    std::cout << '\n';
}

Output:

[t] [e] [s] [t] 
[test]

References

  • C++23 standard (ISO/IEC 14882:2023):
    • 26.5.6 Class template elements_of [range.elementsof]

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