Non-propagating cache(C++20)

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Metaprogramming library(C++11)
General utilities library
Containers library
Iterators library
Ranges library(C++20)
Algorithms library
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Date and time library
Input/output library
Filesystem library(C++17)
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Ranges library

Range access

begin
cbegin
end
cend

rbegin
crbegin
rend
crend

size
ssize
data
cdata

reserve_hint (C++26)
empty

Range conversions
std::from_range_t std::from_range (C++23)(C++23)
to (C++23)

Dangling iterator handling
dangling
borrowed_iterator_t
borrowed_subrange_t

Range primitives

range_size_trange_difference_trange_value_t
elements_of (C++23)

iterator_tconst_iterator_tsentinel_tconst_sentinel_t

(C++23)(C++23)

range_reference_trange_const_reference_trange_rvalue_reference_trange_common_reference_t

(C++23)

Range concepts

range
borrowed_range
common_range

sized_range
viewable_range
view

input_range
output_range
forward_range

bidirectional_range
random_access_range
contiguous_range

approximately_sized_range (C++26)
constant_range (C++23)

empty_viewviews::empty

single_viewviews::single

basic_istream_viewviews::istream

iota_viewviews::iota

repeat_viewviews::repeat

(C++23)(C++23)

Range adaptors

views::all_tviews::all
as_rvalue_viewviews::as_rvalue (C++23)(C++23)
filter_viewviews::filter
transform_viewviews::transform
take_viewviews::take
take_while_viewviews::take_while
common_viewviews::common
views::counted
to_input_viewviews::to_input (C++26)(C++26)

ref_view
drop_viewviews::drop
drop_while_viewviews::drop_while
lazy_split_viewviews::lazy_split
split_viewviews::split
join_viewviews::join
join_with_viewviews::join_with (C++23)(C++23)
concat_viewviews::concat (C++26)(C++26)
cache_latest_viewviews::cache_latest (C++26)(C++26)

owning_view
reverse_viewviews::reverse
as_const_viewviews::as_const (C++23)(C++23)
elements_viewviews::elements
keys_viewviews::keys
values_viewviews::values
enumerate_viewviews::enumerate (C++23)(C++23)
zip_viewviews::zip (C++23)(C++23)
zip_transform_viewviews::zip_transform (C++23)(C++23)

adjacent_viewviews::adjacent (C++23)(C++23)
views::pairwise (C++23)
adjacent_transform_viewviews::adjacent_transform (C++23)(C++23)
views::pairwise_transform (C++23)
chunk_viewviews::chunk (C++23)(C++23)
slide_viewviews::slide (C++23)(C++23)
chunk_by_viewviews::chunk_by (C++23)(C++23)
stride_viewviews::stride (C++23)(C++23)
cartesian_product_viewviews::cartesian_product (C++23)(C++23)

Range generators
std::generator (C++23)

Range adaptor closure objects
range_adaptor_closure (C++23)

Range adaptor objects

Helper items

copyable-box
movable-box

(until C++23) (C++23)

simple-view
*non-propagating-cache*

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template<class T> requiresstd::is_object_v<T> class/non-propagating-cache/;		(since C++20) (exposition only*)

Some range adaptors such asranges::join_view andranges::lazy_split_view conditionally store value (e.g. an iterator) which is specified in terms of an exposition-only class templatenon-propagating-cache.

The wrapper behaves exactly likestd::optional<T>, except that:

it does not copy the value of the source when it is copy constructed or assigned to,
it resets the value of the source when it is moved-from,
it resets its value when it is assigned from, and
it additionally provides a member function template to enable an input view to temporarily cache values as it is iterated over.

The wrapper encapsulates a cache containing a value. Clearing cache is an operation equivalent to resetting a contained value. Such operation is performed when copying or moving a wrapper.

[edit]Template parameters

the type of the contained value, must be an object type

[edit]Member functions

Copy and move constructors

constexpr/non-propagating-cache/ (const/non-propagating-cache/&)noexcept{}	(1)	(since C++20)
constexpr/non-propagating-cache/ (/non-propagating-cache/&& other)noexcept{ other.reset();}	(2)	(since C++20)

1) The copy constructor has no effect.

2) The move constructor clears the cache ofother.

Copy and move assignment operators

constexpr/non-propagating-cache/& operator=(const/non-propagating-cache/& other)noexcept { if(std::addressof(other)!= this) reset(); return*this; }	(1)	(since C++20)
constexpr/non-propagating-cache/& operator=(/non-propagating-cache/&& other)noexcept { reset(); other.reset(); return*this; }	(2)	(since C++20)

1) The copy assignment operator clears the cache of*this.

2) The move assignment operator clears caches of both*this andother.

`non-propagating-cache<T>::emplace-deref`

template<class I> constexpr T&/emplace-deref/(const I& i);		(since C++20) (exposition only*)

Initializes the contained value bydirect-initializing (but not direct-list-initializing) with*i. If*this already contains a value before the call,reset() is called.

Returns a reference to the new contained value.

The program is ill-formed unless the declarationT t(*i); is well-formed for some invented variablet. If*i is a prvalue of possibly cv-qualifiedT, then it is not required to be movable.

Members identical tostd::optional

Member functions

(constructor)	constructs the`optional` object (public member function of`std::optional<T>`)[edit]
(destructor)	destroys the contained value, if there is one (public member function of`std::optional<T>`)[edit]
operator=	assigns contents (public member function of`std::optional<T>`)[edit]
Observers
operator->operator*	accesses the contained value (public member function of`std::optional<T>`)[edit]
operator boolhas_value	checks whether the object contains a value (public member function of`std::optional<T>`)[edit]
Modifiers
reset	destroys any contained value (public member function of`std::optional<T>`)[edit]
emplace	constructs the contained value in-place (public member function of`std::optional<T>`)[edit]

[edit]Notes

non-propagating-cache is used in implementations to cache the result ofbegin() to provide an amortized constant time complexity of the method.

[edit]See also

ranges::join_viewviews::join (C++20)	a`view` consisting of the sequence obtained from flattening a`view` of`range`s (class template)(range adaptor object)[edit]
ranges::join_with_viewviews::join_with (C++23)	a`view` consisting of the sequence obtained from flattening a view of ranges, with the delimiter in between elements (class template)(range adaptor object)[edit]
ranges::split_viewviews::split (C++20)	a`view` over the subranges obtained from splitting another`view` using a delimiter (class template)(range adaptor object)[edit]
ranges::lazy_split_viewviews::lazy_split (C++20)	a`view` over the subranges obtained from splitting another`view` using a delimiter (class template)(range adaptor object)[edit]
ranges::chunk_viewviews::chunk (C++23)	a range of`view`s that are`N`-sized non-overlapping successive chunks of the elements of another`view` (class template)(range adaptor object)[edit]