Difference between revisions of "cpp/iterator/incrementable traits"
From cppreference.com
m (→See also: P1754R1) |
(Links to the definition of “program-defined type”.) |
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| Line 2: | Line 2: | ||
{{cpp/iterator/navbar}} | {{cpp/iterator/navbar}} | ||
{{dcl begin}} | {{dcl begin}} | ||
| − | {{dcl header | iterator}} | + | {{dcl header|iterator}} |
| − | {{dcl | num=1 | since=c++20 | | + | {{dcl|num=1|since=c++20| |
template< class I > | template< class I > | ||
| − | struct incrementable_traits { }; | + | struct incrementable_traits {}; |
}} | }} | ||
| − | {{dcl | num=2 | since=c++20 | | + | {{dcl|num=2|since=c++20| |
template< class T > | template< class T > | ||
requires std::is_object_v<T> | requires std::is_object_v<T> | ||
struct incrementable_traits<T*>; | struct incrementable_traits<T*>; | ||
}} | }} | ||
| − | {{dcl | num=3 | since=c++20 | | + | {{dcl|num=3|since=c++20| |
template< class T > | template< class T > | ||
| − | struct incrementable_traits<const T> : incrementable_traits<T> { }; | + | struct incrementable_traits<const T> : incrementable_traits<T> {}; |
}} | }} | ||
| − | {{dcl | num=4 | since=c++20 | | + | {{dcl|num=4|since=c++20| |
template< class T > | template< class T > | ||
requires requires { typename T::difference_type; } | requires requires { typename T::difference_type; } | ||
struct incrementable_traits<T>; | struct incrementable_traits<T>; | ||
}} | }} | ||
| − | {{dcl | num=5 | since=c++20 | | + | {{dcl|num=5|since=c++20| |
template< class T > | template< class T > | ||
requires (!requires { typename T::difference_type; }) && | requires (!requires { typename T::difference_type; }) && | ||
| Line 29: | Line 29: | ||
{{dcl end}} | {{dcl end}} | ||
| − | Computes the associated difference type of the type {{tt|I}}, if any. | + | Computes the associated difference type of the type {{tt|I}}, if any. A program may specialize {{tt|incrementable_traits}} for a {{lsd|cpp/language/type#Program-defined type}}. |
@1@ Primary template is an empty struct. | @1@ Primary template is an empty struct. | ||
| − | @2@ Specialization for pointers. Provides a member type {{tt|difference_type}} | + | |
| + | @2@ Specialization for pointers. | ||
| + | @@ Provides a member type {{tt|difference_type}} same as {{lc|std::ptrdiff_t}}. | ||
| + | |||
@3@ Specialization for const-qualified types. | @3@ Specialization for const-qualified types. | ||
| − | @4@ Specialization for types that define a public and accessible member type {{tt|difference_type}}. Provides a member type {{tt|difference_type}} | + | |
| − | @5@ Specialization for types that do not define a public and accessible member type {{tt|difference_type}} but do support subtraction. Provides a member type {{tt|difference_type}} | + | @4@ Specialization for types that define a public and accessible member type {{tt|difference_type}}. |
| + | @@ Provides a member type {{tt|difference_type}} same as {{tt|T::difference_type}}. | ||
| + | |||
| + | @5@ Specialization for types that do not define a public and accessible member type {{tt|difference_type}} but do support subtraction. | ||
| + | @@ Provides a member type {{tt|difference_type}} same as {{c/core|std::make_signed_t<decltype(std::declval<T>() - std::declval<T>())>}}. The implicit expression variations rule (see below) applies to the expression {{c|a - b}}. | ||
{{cpp/concepts/implicit expression variations}} | {{cpp/concepts/implicit expression variations}} | ||
| Line 44: | Line 51: | ||
===See also=== | ===See also=== | ||
{{dsc begin}} | {{dsc begin}} | ||
| − | {{dsc inc | cpp/iterator/dsc weakly_incrementable}} | + | {{dsc inc|cpp/iterator/dsc weakly_incrementable}} |
| − | {{dsc inc | cpp/iterator/dsc iter_t}} | + | {{dsc inc|cpp/iterator/dsc iter_t}} |
| − | {{dsc inc | cpp/iterator/dsc iterator_traits}} | + | {{dsc inc|cpp/iterator/dsc iterator_traits}} |
{{dsc end}} | {{dsc end}} | ||
{{langlinks|de|es|ja|ru|zh}} | {{langlinks|de|es|ja|ru|zh}} | ||
Revision as of 23:09, 12 March 2024
| Defined in header <iterator>
|
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| template< class I > struct incrementable_traits {}; |
(1) | (since C++20) |
| template< class T > requires std::is_object_v<T> |
(2) | (since C++20) |
| template< class T > struct incrementable_traits<const T> : incrementable_traits<T> {}; |
(3) | (since C++20) |
| template< class T > requires requires { typename T::difference_type; } |
(4) | (since C++20) |
| template< class T > requires (!requires { typename T::difference_type; }) && |
(5) | (since C++20) |
Computes the associated difference type of the type I, if any. A program may specialize incrementable_traits for a program-defined type.
1) Primary template is an empty struct.
2) Specialization for pointers.
Provides a member type
difference_type same as std::ptrdiff_t.3) Specialization for const-qualified types.
4) Specialization for types that define a public and accessible member type
difference_type. Provides a member type
difference_type same as T::difference_type.5) Specialization for types that do not define a public and accessible member type
difference_type but do support subtraction. Provides a member type
difference_type same as std::make_signed_t<decltype(std::declval<T>() - std::declval<T>())>. The implicit expression variations rule (see below) applies to the expression a - b.Implicit expression variations
A requires expression that uses an expression that is non-modifying for some constant lvalue operand also requires implicit expression variations.
Example
| This section is incomplete Reason: no example |
See also
| (C++20) |
specifies that a semiregular type can be incremented with pre- and post-increment operators (concept) |
| (C++20)(C++20)(C++23)(C++20)(C++20)(C++20) |
computes the associated types of an iterator (alias template) |
| provides uniform interface to the properties of an iterator (class template) |
