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Showing content from https://en.cppreference.com/w/cpp/language/../numeric/../string/../ranges/view.html below:

std::ranges::view, std::ranges::enable_view, std::ranges::view_base - cppreference.com

struct view_base { };

The

concept specifies the requirements of a

type that has suitable semantic properties for use in constructing range adaptor pipelines.

The

variable template is used to indicate whether a

is a

.

is

if and only if

has exactly one public base class

for some type

, and

has no base classes of type

for any other type

.

Users may specialize

to

for cv-unqualified program-defined types which model

, and

for types which do not. Such specializations must be

and have type

.

Deriving from

enables

types to model

.

models

only if:

• move construction of T has constant time complexity, and
• if \(\scriptsize N\)N copies and/or moves are made from a T object holding \(\scriptsize M\)M elements, then these \(\scriptsize N\)N objects have \(\scriptsize \mathcal{O}{(N+M)}\)𝓞(N+M) destruction (which implies that a moved-from view object has \(\scriptsize \mathcal{O}{(1)}\)𝓞(1) destruction), and
• either std::copy_constructible<T> is false, or copy construction of T has constant time complexity, and
• either std::copyable<T> is false, or copy assignment of T has no more time complexity than destruction followed by copy construction.

Specializations of enable_view for all specializations of the following standard templates are defined as true:

• std::basic_string_view
• std::span

Examples of view types are:

• A range type that wraps a pair of iterators, e.g., std::ranges::subrange<I>.
• A range type that holds its elements by std::shared_ptr and shares ownership with all its copies.
• A range type that generates its elements on demand, e.g., std::ranges::iota_view.

A copyable container such as std::vector<std::string> generally does not meet the semantic requirements of view since copying the container copies all of the elements, which cannot be done in constant time.

While views were originally described as cheaply copyable and non-owning ranges, a type is not required to be copyable or non-owning for it to model view. However, it must still be cheap to copy (if it is copyable), move, assign, and destroy, so that range adaptors will not have unexpected complexity.

By default, a type modeling movable and range is considered a view if it is publicly and unambiguously derived from view_base, or exactly one specialization of std::ranges::view_interface.

A minimum view.

#include <ranges>
 
struct ArchetypalView : std::ranges::view_interface<ArchetypalView>
{
    int* begin();
    int* end();
};
 
static_assert(std::ranges::view<ArchetypalView>);

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

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