std::ranges::views::transform,std::ranges::transform_view(3)

NAME
std::ranges::views::transform,std::ranges::transform_view - std::ranges::views::transform,std::ranges::transform_view

Synopsis
   Defined in header <ranges>
   template< ranges::input_range V,
   std::copy_constructible F >
   requires ranges::view<V> &&
   std::is_object_v<F> && (1) (since C++20)
   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>>
   namespace views {
   inline constexpr /*unspecified*/ transform = /*unspecified*/; (2) (since C++20)
   }
   Call signature
   template< ranges::viewable_range R, class F >
   requires /* see below */ (since C++20)
   constexpr ranges::view auto transform( R&& r, F&& fun );
   template< class F > (since C++20)
   constexpr /*range adaptor closure*/ transform( F&& fun );
   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.
  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)).

Member functions
   constructor constructs a transform_view
   (C++20) (public member function)
   base returns a copy of the underlying (adapted) view
   (C++20) (public member function)
   begin returns an iterator to the beginning
   (C++20) (public member function)
   end returns an iterator or a sentinel to the end
   (C++20) (public member function)
   size returns the number of elements. Provided only if the underlying
   (C++20) (adapted) range satisfies sized_range.
                 (public member function)
         Inherited from std::ranges::view_interface
   empty Returns whether the derived view is empty. Provided if it satisfies
   (C++20) sized_range or forward_range.
                 (public member function of std::ranges::view_interface<D>)
   operator bool Returns whether the derived view is not empty. Provided if
   (C++20) ranges::empty is applicable to it.
                 (public member function of std::ranges::view_interface<D>)
   front Returns the first element in the derived view. Provided if it
   (C++20) satisfies forward_range.
                 (public member function of std::ranges::view_interface<D>)
   back Returns the last element in the derived view. Provided if it satisfies
   (C++20) bidirectional_range and common_range.
                 (public member function of std::ranges::view_interface<D>)
   operator[] Returns the nth element in the derived view. Provided if it satisfies
   (C++20) random_access_range.
                 (public member function of std::ranges::view_interface<D>)
  Deduction guides
  Nested classes
   iterator the iterator type
   (C++20) (exposition-only member class template)
   sentinel the sentinel type
   (C++20) (exposition-only member class template)

Example
// Run this code
 #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

See also
   ranges::transform applies a function to a range of elements
   (C++20) (niebloid)