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Standard Template Library Programmer's Guide
(document number: 007-3426-004 / published: 1999-05-21) table of contents | additional info | download
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Pair Associative Container


Category: containers	Component type: concept

Description

A Pair Associative Container is an Associative Container that associates a key with some other object. The value type of a Pair Associative Container is pair<const key_type, data_type>. [1]

Refinement of

Associative Container

Associated types

One new type is introduced, in addition to the types defined in the Associative Container requirements. Additionally, Pair Associative Container introduces one new type restriction

Key type	`X::key_type`	The type of the key associated with `X::value_type`.
Data type	`X::data_type`	The type of the data associated with `X::value_type`. A Pair Associative Container can be thought of as a mapping from `key_type` to `data_type`.
Value type	`X::value_type`	The type of object stored in the container. The value type is required to be `pair<const key_type, data_type>`.

Notation

`X`	A type that is a model of Pair Associative Container
`a`	Object of type `X`
`t`	Object of type `X::value_type`
`d`	Object of type `X::data_type`
`k`	Object of type `X::key_type`
`p`, `q`	Object of type `X::iterator`

Definitions

Valid expressions

None, except for those defined in the Associative Container requirements.

Expression semantics

Complexity guarantees

Invariants

Models

Notes

[1] The value type must be pair<const key_type, data_type>, rather than pair<key_type, data_type>, because of the Associative Container invariant of key immutability. The data_type part of an object in a Pair Associative Container may be modified, but the key_type part may not be. Note the implication of this fact: a Pair Associative Container cannot provide mutable iterators (as defined in the Trivial Iterator requirements), because the value type of a mutable iterator must be Assignable, and pair<const key_type, data_type> is not Assignable. However, a Pair Associative Container can provide iterators that are not completely constant: iterators such that the expression (*i).second = d is valid.