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

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< cpp‎ | ranges
 
 
Ranges library
Range access
Range conversions
(C++23)
Range primitives



Dangling iterator handling
Range concepts
Views

Factories




Adaptors
Range adaptor objects
Range adaptor closure objects
Helper items
 
 
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)
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.
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.

Contents

[edit] Expression-equivalent

Expression e is expression-equivalent to expression f, if

  • e and f have the same effects, and
  • either both are constant subexpressions or else neither is a constant subexpression, and
  • either both are potentially-throwing or else neither is potentially-throwing (i.e. noexcept(e) == noexcept(f)).

[edit] Member functions

constructs a transform_view
(public member function) [edit]
(C++20)
returns a copy of the underlying (adapted) view
(public member function) [edit]
(C++20)
returns an iterator to the beginning
(public member function) [edit]
(C++20)
returns an iterator or a sentinel to the end
(public member function) [edit]
(C++20)
returns the number of elements. Provided only if the underlying (adapted) range satisfies sized_range.
(public member function) [edit]
Inherited from std::ranges::view_interface
(C++20)
Returns whether the derived view is empty. Provided if it satisfies sized_range or forward_range.
(public member function of std::ranges::view_interface<D>) [edit]
Returns whether the derived view is not empty. Provided if ranges::empty is applicable to it.
(public member function of std::ranges::view_interface<D>) [edit]
(C++20)
Returns the first element in the derived view. Provided if it satisfies forward_range.
(public member function of std::ranges::view_interface<D>) [edit]
(C++20)
Returns the last element in the derived view. Provided 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 if it satisfies random_access_range.
(public member function of std::ranges::view_interface<D>) [edit]

[edit] Deduction guides

[edit] Nested classes

(C++20)
the iterator type
(exposition-only member class template)
(C++20)
the sentinel type
(exposition-only member class template)

[edit] 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 (x >= 'A' && x <= 'Z') {
        return rot13a(x, 'A');
    }
 
    if (x >= 'a' && x <= 'z') {
        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

[edit] See also

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