Namespaces
Variants
Views
Actions

Difference between revisions of "cpp/named req/Container"

From cppreference.com
< cpp‎ | named req
(Added LWG issue #276 DR (part 1/2).)
(Added LWG issue #322 DR.)
Line 7: Line 7:
 
* {{tt|T}}, an element type;
 
* {{tt|T}}, an element type;
 
* {{tt|C}}, a {{named req/core|Container}} type containing elements of type {{tt|T}};
 
* {{tt|C}}, a {{named req/core|Container}} type containing elements of type {{tt|T}};
−
* {{tt|a}} and {{tt|b}}, objects of type {{tt|C}};
+
* {{c|a}} and {{c|b}}, objects of type {{tt|C}};
−
* {{tt|rv}}, a prvalue expression of type {{tt|C}}.
+
* {{c|rv}}, a prvalue expression of type {{tt|C}}.
  
 
====Types====
 
====Types====
Line 18: Line 18:
 
|{{tt|reference}}||{{tt|T&}}||
 
|{{tt|reference}}||{{tt|T&}}||
 
|-
 
|-
−
|{{tt|const_reference}}||{{tt|const T&}}||
+
|{{tt|const_reference}}||{{c/core|const T&}}||
 
|-
 
|-
−
|{{tt|iterator}}||iterator pointing to {{tt|T}}||{{named req|ForwardIterator}}<br/>convertible to {{tt|const_iterator}}
+
|{{tt|iterator}}||iterator whose [[cpp/iterator#Types and writability|value type]] is {{tt|T}}||{{named req|ForwardIterator}}<br>convertible to {{tt|const_iterator}}
 
|-
 
|-
−
|{{tt|const_iterator}}||constant iterator pointing to {{tt|T}}||{{named req|ForwardIterator}}
+
|{{tt|const_iterator}}||constant iterator whose [[cpp/iterator#Types and writability|value type]] is {{tt|T}}||{{named req|ForwardIterator}}
 
|-
 
|-
 
|{{tt|difference_type}}||signed integer
 
|{{tt|difference_type}}||signed integer
Line 44: Line 44:
 
|{{c|1=a = rv}}||{{tt|C&}}||destroys or move-assigns all elements of {{c|a}} from elements of {{c|rv}}||Post: if {{c|a}} and {{c|rv}} do not refer the same object, {{c|a}} is equal to the value {{c|rv}} had before this assignment||Linear
 
|{{c|1=a = rv}}||{{tt|C&}}||destroys or move-assigns all elements of {{c|a}} from elements of {{c|rv}}||Post: if {{c|a}} and {{c|rv}} do not refer the same object, {{c|a}} is equal to the value {{c|rv}} had before this assignment||Linear
 
|-
 
|-
−
|{{c|a.~C()}}||{{c|void}}||destroys all elements of {{c|a}} and frees all memory||  ||Linear
+
|{{c|a.~C()}}||{{c/core|void}}||destroys all elements of {{c|a}} and frees all memory||  ||Linear
 
|-
 
|-
 
|{{c|a.begin()}}||{{tt|(const_)iterator}}||Iterator to the first element of {{c|a}}|| ||Constant
 
|{{c|a.begin()}}||{{tt|(const_)iterator}}||Iterator to the first element of {{c|a}}|| ||Constant
Line 54: Line 54:
 
|{{c|a.cend()}}<br>{{mark since c++11}}||{{tt|const_iterator}}||{{c|const_cast<const C&>(a).end()}}|| ||Constant
 
|{{c|a.cend()}}<br>{{mark since c++11}}||{{tt|const_iterator}}||{{c|const_cast<const C&>(a).end()}}|| ||Constant
 
|-
 
|-
−
|{{c|1=a == b}} || convertible to {{c|bool}} || {{rev begin}}
+
|{{c|1=a == b}} || convertible to {{c/core|bool}} || {{rev begin}}
 
{{rev|until=c++14|{{c|1=a.size() == b.size() &&
 
{{rev|until=c++14|{{c|1=a.size() == b.size() &&
 
     std::equal(a.begin(),
 
     std::equal(a.begin(),
Line 63: Line 63:
 
|| Pre: {{tt|T}} must be {{named req|EqualityComparable}} || Constant<ref>always linear for {{lc|std::forward_list}}</ref> if {{c|1=a.size() !=}}<br>{{c|b.size()}}, linear otherwise<!-- LWG2257 -->
 
|| Pre: {{tt|T}} must be {{named req|EqualityComparable}} || Constant<ref>always linear for {{lc|std::forward_list}}</ref> if {{c|1=a.size() !=}}<br>{{c|b.size()}}, linear otherwise<!-- LWG2257 -->
 
|-
 
|-
−
|{{c|1=a != b}} || convertible to {{c|bool}} || {{c|1=!(a == b)}} || || Linear
+
|{{c|1=a != b}} || convertible to {{c/core|bool}} || {{c|1=!(a == b)}} || || Linear
 
|-
 
|-
−
|{{c|a.swap(b)}} || {{c|void}} || exchanges the values of {{c|a}} and {{c|b}} ||  
+
|{{c|a.swap(b)}} || {{c/core|void}} || exchanges the values of {{c|a}} and {{c|b}} ||  
 
| Constant<ref name="array">{{mark since c++11}} Linear for {{lc|std::array}}</ref><ref name="should">{{mark until c++11}} Not strictly constant</ref>
 
| Constant<ref name="array">{{mark since c++11}} Linear for {{lc|std::array}}</ref><ref name="should">{{mark until c++11}} Not strictly constant</ref>
 
|-
 
|-
−
|{{c|swap(a, b)}} || {{c|void}} || {{c|a.swap(b)}} || || Constant<ref name="array"/>
+
|{{c|swap(a, b)}} || {{c/core|void}} || {{c|a.swap(b)}} || || Constant<ref name="array"/>
 
|-
 
|-
 
|{{c|a.size()}} || {{tt|size_type}} || {{c|std::distance(a.begin(), a.end())}} || || Constant<ref name="should" />
 
|{{c|a.size()}} || {{tt|size_type}} || {{c|std::distance(a.begin(), a.end())}} || || Constant<ref name="should" />
Line 74: Line 74:
 
|{{c|a.max_size()}} || {{tt|size_type}} || {{c|b.size()}} where {{c|b}} is the largest possible container || || Constant<ref name="should" />
 
|{{c|a.max_size()}} || {{tt|size_type}} || {{c|b.size()}} where {{c|b}} is the largest possible container || || Constant<ref name="should" />
 
|-
 
|-
−
|{{c|a.empty()}} || convertible to {{c|bool}} || {{c|1=a.begin() == a.end()}} || || Constant
+
|{{c|a.empty()}} || convertible to {{c/core|bool}} || {{c|1=a.begin() == a.end()}} || || Constant
 
|-
 
|-
 
!colspan=6|notes
 
!colspan=6|notes
Line 103: Line 103:
 
{{dr list item|wg=lwg|dr=179|std=C++98|before={{tt|iterator}} and {{tt|const_iterator}} types might be incomparable|after=required to be comparable}}
 
{{dr list item|wg=lwg|dr=179|std=C++98|before={{tt|iterator}} and {{tt|const_iterator}} types might be incomparable|after=required to be comparable}}
 
{{dr list item|wg=lwg|dr=276|std=C++98|before={{tt|T}} was required to be {{named req|CopyAssignable}}|after={{tt|T}} is required to be {{named req|CopyConstructible}}}}
 
{{dr list item|wg=lwg|dr=276|std=C++98|before={{tt|T}} was required to be {{named req|CopyAssignable}}|after={{tt|T}} is required to be {{named req|CopyConstructible}}}}
 +
{{dr list item|wg=lwg|dr=322|std=C++98|before=the value types of {{tt|iterator}} and {{tt|const_iterator}} were not specified|after=specified as {{tt|T}}}}
 
{{dr list item|wg=lwg|dr=2263|std=C++11|before=the resolution of {{lwg|179}} was accidentally dropped in C++11|after=restored}}
 
{{dr list item|wg=lwg|dr=2263|std=C++11|before=the resolution of {{lwg|179}} was accidentally dropped in C++11|after=restored}}
 
{{dr list item|wg=lwg|dr=2839|std=C++11|before=self move assignment of standard containers was not allowed|after=allowed but the result is unspecifed}}
 
{{dr list item|wg=lwg|dr=2839|std=C++11|before=self move assignment of standard containers was not allowed|after=allowed but the result is unspecifed}}

Revision as of 00:48, 11 January 2023

 
C++
 
C++ named requirements
 

A Container is an object used to store other objects and taking care of the management of the memory used by the objects it contains.

Contents

Requirements

  • T, an element type;
  • C, a Container type containing elements of type T;
  • a and b, objects of type C;
  • rv, a prvalue expression of type C.

Types

Name Type Requirements
value_type T CopyConstructible(until C++11)Erasable(since C++11)
reference T&
const_reference const T&
iterator iterator whose value type is T LegacyForwardIterator
convertible to const_iterator
const_iterator constant iterator whose value type is T LegacyForwardIterator
difference_type signed integer must be the same as iterator_traits::difference_type for iterator and const_iterator
size_type unsigned integer large enough to represent all positive values of difference_type

Methods and operators

Expression Return type Semantics Conditions Complexity
C() C creates an empty container Post: C().empty()
== true		 Constant
C(a) C creates a copy of a Pre: T must be CopyInsertable
Post: a == C(a)		 Linear
C(rv)
(since C++11)		 C moves rv Post: equal to the value rv had before this construction Constant[1]
a = b C& destroys or copy-assigns all elements of a from elements of b Post: a == b Linear
a = rv C& destroys or move-assigns all elements of a from elements of rv Post: if a and rv do not refer the same object, a is equal to the value rv had before this assignment Linear
a.~C() void destroys all elements of a and frees all memory Linear
a.begin() (const_)iterator Iterator to the first element of a Constant
a.end() (const_)iterator Iterator to one past the last element of a Constant
a.cbegin()
(since C++11)		 const_iterator const_cast<const C&>(a).begin() Constant
a.cend()
(since C++11)		 const_iterator const_cast<const C&>(a).end() Constant
a == b convertible to bool
a.size() == b.size() &&

    std::equal(a.begin(),

        a.end(), b.begin())		 (until C++14)
std::equal(a.begin(), a.end(),
    b.begin(), b.end())		 (since C++14)
 Pre: T must be EqualityComparable Constant[2] if a.size() !=
b.size(), linear otherwise
a != b convertible to bool !(a == b) Linear
a.swap(b) void exchanges the values of a and b Constant[1][3]
swap(a, b) void a.swap(b) Constant[1]
a.size() size_type std::distance(a.begin(), a.end()) Constant[3]
a.max_size() size_type b.size() where b is the largest possible container Constant[3]
a.empty() convertible to bool a.begin() == a.end() Constant
notes
  1. ↑ 1.0 1.1 1.2 Linear for std::array
  2. ↑ always linear for std::forward_list
  3. ↑ 3.0 3.1 3.2 (until C++11) Not strictly constant

Given

  • i and j, objects of a container's iterator type,

in the expressions i == j, i != j, i < j, i <= j, i >= j, i > j, i - j, either or both may be replaced by an object of the container's const_iterator type referring to the same element with no change in semantics.

Container data races

see container thread safety

Other requirements

C
T

Defect reports

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

DR Applied to Behavior as published Correct behavior
LWG 179 C++98 iterator and const_iterator types might be incomparable required to be comparable
LWG 276 C++98 T was required to be CopyAssignable T is required to be CopyConstructible
LWG 322 C++98 the value types of iterator and const_iterator were not specified specified as T
LWG 2263 C++11 the resolution of LWG issue 179 was accidentally dropped in C++11 restored
LWG 2839 C++11 self move assignment of standard containers was not allowed allowed but the result is unspecifed

See also

C++ documentation for Containers library
Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/named_req/Container&oldid=146313"