std::ranges::views::as_const, std::ranges::as_const_view

Since C++23

Header: <ranges>

  1. A range adaptor that represents a view of underlying view that is also a constant_range. An as_const_view always has read-only elements (if not empty).

# Declarations

template< ranges::view V >
requires ranges::input_range<V>
class as_const_view
: public ranges::view_interface<as_const_view<V>>

(since C++23)

namespace views {
inline constexpr /* unspecified */ as_const = /* unspecified */;
}

(since C++23)

Call signature

template< ranges::viewable_range R >
requires /* see below */
constexpr ranges::view auto as_const( R&& r );

(since C++23)

# Parameters

# Notes

Feature-test macro Value Std Feature __cpp_lib_ranges_as_const 202207L (C++23) ranges::as_const_view, std::const_iterator

# Example

#include <cassert>
#include <ranges>
 
int main()
{
    int x[]{1, 2, 3, 4, 5};
 
    auto v1 = x | std::views::drop(2);
    assert(v1.back() == 5);
    v1[0]++; // OK, can modify non-const element
 
    auto v2 = x | std::views::drop(2) | std::views::as_const;
    assert(v2.back() == 5);
    // v2[0]++; // Compile-time error, cannot modify read-only element
}

# See also