std::ranges::view_interface<D>::front

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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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std::ranges::view_interface

Member functions
empty
cbegin (C++23)
cend (C++23)
operator bool
data
size
front
back
operator[]

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constexpr decltype(auto) front() requiresranges::forward_range<D>;	(1)	(since C++20)
constexpr decltype(auto) front()const requiresranges::forward_range<const D>;	(2)	(since C++20)

The default implementation offront() member function returns the first element in the view of the derived type. Whether the element is returned by value or by reference depends on theoperator* of the iterator type.

1) Letderived bestatic_cast<D&>(*this). Equivalent toreturn*ranges::begin(derived);. The behavior is undefined ifempty() istrue (i.e. the beginning iterator compares equal to the sentinel), even if the iterator obtained in the same way is dereferenceable.

2) Same as(1), except thatderived isstatic_cast<const D&>(*this).

[edit]Return value

The first element in the view.

[edit]Notes

In C++20, no type derived fromstd::ranges::view_interface in the standard library provides their ownfront() member function. Almost all of these types use the default implementation.

A notable exception isstd::ranges::basic_istream_view. For it never satisfiesforward_range, the view cannot use the inheritedfront().

The inheritedfront() member function is available forstd::ranges::empty_view, but a call to it always results in undefined behavior.

[edit]Example

This section is incomplete
Reason: no example

[edit]See also

begincbegin (C++11)(C++14)	returns an iterator to the beginning of a container or array (function template)[edit]
ranges::begin (C++20)	returns an iterator to the beginning of a range (customization point object)[edit]
ranges::cbegin (C++20)	returns an iterator to the beginning of a read-only range (customization point object)[edit]