std::ranges::views::take_while, std::ranges::take_while_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::view V, class Pred >

    requires ranges::input_range<V> &&
             std::is_object_v<Pred> &&
             std::indirect_unary_predicate<const Pred, ranges::iterator_t<V>>

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

    inline constexpr /*unspecified*/ take_while = /*unspecified*/;

}
(2) (since C++20)
Call signature
template< ranges::viewable_range R, class Pred >

    requires /* see below */

constexpr ranges::view auto take_while( R&& r, Pred&& pred );
(since C++20)
template< class Pred >
constexpr /*range adaptor closure*/ take_while( Pred&& pred );
(since C++20)
1) A range adaptor that represents view of the elements from an underlying sequence, starting at the beginning and ending at the first element for which the predicate returns false.
2) Range adaptor object. The expression views::take_while(e, f) is expression-equivalent to take_while_view(e, f) for any suitable subexpressions e and f.

take_while_view models the concepts contiguous_range, random_access_range, bidirectional_range, forward_range, and input_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

constructs a take_while_view
(public member function)
(C++20)
returns a copy of the underlying (adapted) view
(public member function)
(C++20)
returns a reference to the stored predicate
(public member function)
(C++20)
returns an iterator to the beginning
(public member function)
(C++20)
returns a sentinel representing the end
(public member function)
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>)
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>)
(C++20)
Gets the address of derived view's data. Provided if its iterator type satisfies contiguous_iterator.
(public member function of std::ranges::view_interface<D>)
(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>)
Returns the nth element in the derived view. Provided if it satisfies random_access_range.
(public member function of std::ranges::view_interface<D>)

Deduction guides

Nested classes

the sentinel type
(exposition-only member class template)

Example

#include <ranges>
#include <iostream>
 
int main()
{
    for (int year : std::views::iota(2017)
                  | std::views::take_while([](int y) { return y <= 2020; })) {
        std::cout << year << ' ';
    }
    std::cout << '\n';
 
    const char idea[] {"Today is yesterday's tomorrow!.."};
    for (char x : std::ranges::take_while_view(idea, [](char c) { return c != '.'; })) {
        std::cout << x;
    }
    std::cout << '\n';
}

Output:

2017 2018 2019 2020 
Today is yesterday's tomorrow!

See also

a view consisting of the first N elements of another view
(class template) (range adaptor object)
a view consisting of the elements of another view, skipping the initial subsequence of elements until the first element where the predicate returns false
(class template) (range adaptor object)