Concepts / Standard Template Library Programmer / Библиотека (книги, учебники и журналы) / В помощь Веб-Мастеру

Обложка
Аннотация

Книга: Standard Template Library Programmer

Concepts

Разделы на этой странице:

Description
Notation
Valid expressions
Expression semantics
Models
Notes
See also

Assignable

Category: utilities

Component type: concept

Description

A type is Assignable if it is possible to copy objects of that type and to assign values to variables.

Notation

X A type that is a model of Assignable

x, y Object of type X

Valid expressions

Name	Expression	Return type
Copy constructor	`X(x)`	`X`
Copy constructor	`X x(y); X x = y;`
Assignment	`x = y` [1]	`X&`
Swap	`swap(x,y)`	`void`

Expression semantics

Name	Expression	Semantics
Copy constructor	`X(x)`	X(x) is a copy of x [2]
Copy constructor	`X(x)`	X(x) is a copy of x [2]
Copy constructor	`X x(y); X x = y;`	x is a copy of y [2]
Assignment	`x = y` [1]	x is a copy of y [2]
Swap	`swap (x,y)`	Equivalent to`{ X tmp = x; x = y; y = tmp; }`

Models

• int

Notes

[1] One implication of this requirement is that a const type is not Assignable. For example, const int is not Assignable: if x is declared to be of type const int, then x = 7 is illegal. Similarly, the type pair<const int, int> is not Assignable.

[2] The reason this says "x is a copy of y ", rather than "x == y ", is that operator== is not necessarily defined: equality is not a requirement of Assignable. If the type X is EqualityComparable as well as Assignable, then a copy of x should compare equal to x.