Assignable

Description

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

Refinement Of

Associated Type(s)

Notation

X	A type that is a model of Assignable
x, y	Object of type X

Definitions

Valid Expressions

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

Expression Semantics

Name	Expression	Precondition	Semantics	Postcondition
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	adobe::swap(x,y)[3]		Equivalent to { X tmp = x; x = y; y = tmp; }

Complexity Guarantee(s)

Invariants

Type(s) Modeling this Concept

• 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.

See Also

• DefaultConstructible
• EqualityComparable