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std::ranges::views::transform, std::ranges::transform_view - cppreference.com

From cppreference.com

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)
(until C++23)		 
template< ranges::input_range V,
          std::move_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>>
(since C++23) 
namespace views {
    inline constexpr /*unspecified*/ transform = /*unspecified*/;
}
(2) (since C++20)

Call signature

 
template< ranges::viewable_range R, class F >
    requires /* see below */
constexpr ranges::view auto transform( R&& r, F&& fun );
(since C++20) 
template< class F >
constexpr /*range adaptor closure*/ transform( F&& fun );
(since C++20)

1) A range adaptor that represents

view

of an underlying sequence after applying a transformation function to each element.

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.

Data members

Member Description
V base_ (private) the underlying view
(exposition-only member object*)
fun_ (private) the underlying function object
(exposition-only member object*)

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]
returns the approximate size of the resulting approximately_sized_range
(public member function) [edit]
Inherited from ranges::view_interface
returns whether the derived view is empty, provided only if it satisfies sized_range or forward_range
(public member function of std::ranges::view_interface<D>) [edit]

(C++23)

 returns a constant iterator to the beginning of the range
(public member function of std::ranges::view_interface<D>) [edit]

(C++23)

 returns a sentinel for the constant iterator of the range
(public member function of std::ranges::view_interface<D>) [edit]
returns whether the derived view is not empty, provided only if ranges::empty is applicable to it
(public member function of std::ranges::view_interface<D>) [edit]
returns the first element in the derived view, provided if it satisfies forward_range
(public member function of std::ranges::view_interface<D>) [edit]
returns the last element in the derived view, provided only if it satisfies bidirectional_range and common_range
(public member function of std::ranges::view_interface<D>) [edit]
returns the nth element in the derived view, provided only if it satisfies random_access_range
(public member function of std::ranges::view_interface<D>) [edit]

Deduction guides

Nested classes

the iterator type
(exposition-only member class template*)
the sentinel type
(exposition-only member class template*)

Example

#include <algorithm>
#include <cstdio>
#include <iterator>
#include <ranges>
#include <string>
 
char rot13a(const char x, const char a)
{
    return a + (x - a + 13) % 26;
}

char rot13(const char x)
{
    if ('Z' >= x and x >= 'A')
        return rot13a(x, 'A');

    if ('z' >= x and x >= 'a')
        return rot13a(x, 'a');

    return x;
}
 
int main()
{
    auto show = [](const unsigned char x) { std::putchar(x); };
 
    std::string in{"cppreference.com\n"};
    std::ranges::for_each(in, show);
    std::ranges::for_each(in | std::views::transform(rot13), show);
 
    std::string out;
    std::ranges::copy(std::views::transform(in, rot13), std::back_inserter(out));
    std::ranges::for_each(out, show);
    std::ranges::for_each(out | std::views::transform(rot13), show);
}

Output: 

cppreference.com
pccersrerapr.pbz
pccersrerapr.pbz
cppreference.com

See also