std::ranges::views::transform, std::ranges::transform_view

< cpp‎ | ranges
Defined in header <ranges>
template< ranges::input_range V,

          std::copy_constructible F >
  requires ranges::view<V> &&
           std::is_object_v<F> &&
           std::regular_invocable<F&, ranges::range_reference_t<V>> &&
           /* invoke_result_t<F&, range_reference_t<V>>& is a valid type */

class transform_view : public ranges::view_interface<transform_view<V, F>>
(1) (since C++20)
namespace views {

    inline constexpr /*unspecified*/ transform = /*unspecified*/;

(2) (since C++20)
1) A range adaptor that represents view of an underlying sequence after applying a transformation function to each element.
2) Range adaptor object. The expression views::transform(E, F) is expression-equivalent to transform_view{E, F} for any suitable subexpressions E and F.

transform_view models the concepts random_access_range, bidirectional_range, forward_range, input_range, common_range, and sized_range when the underlying view V models respective concepts.


[edit] Expression-equivalent

Expression e is expression-equivalent to expression f, if e and f have the same effects, either are both potentially-throwing or are both not potentially-throwing (i.e. noexcept(e) == noexcept(f)), and either are both constant subexpressions or are both not constant subexpressions.

[edit] Member functions

constructs a transform_view
(public member function) [edit]
returns a copy of the underlying (adapted) view
(public member function) [edit]
returns an iterator to the beginning
(public member function) [edit]
returns an iterator or a sentinel to the end
(public member function) [edit]
returns the number of elements. Provided only if the underlying (adapted) range satisfies sized_range
(public member function) [edit]

[edit] Deduction guides

[edit] Nested classes

the iterator type
(public member class)
the sentinel type
(public member class)

[edit] Example

#include <algorithm>
#include <array>
#include <cstdio>
#include <ranges>
#include <string>
class Transcoder {
    static constexpr std::array r{
        0x02,-0x02,-0x42, 0x05, 0x04, 0x05, 0x04,-0x02,
        0x00,-0x0a, 0x06,-0x04, 0x00, 0x0c, 0x03,-0x06,
    decltype(r.size()) p{}, q{};
    char operator() (int x) {
        ! (p|q)
        ? (99 == x ? x += r[p++]  : x -= r[q++])
        : (0 < p && p < r.size()) ? x += r[p++]
        : (0 < q && q < r.size()) ? x -= r[q++]
        : (0)
        return x;
int main()
    auto show = [](const char x) { std::putchar(x); };
    std::string in{ "\n" };
    std::ranges::for_each(in, show);
    std::string out;
        std::ranges::views::transform(in, Transcoder{}),
    std::ranges::for_each(out, show);
    auto view = std::ranges::transform_view{ out, Transcoder{} };
    std::ranges::for_each(view, show);
    std::ranges::for_each(view, show);


[edit] See also

applies a function to a range of elements
(niebloid) [edit]