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.
Refinement of
Associated types
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

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

swap(x,y)


Equivalent to
{
X tmp = x;
x = y;
y = tmp;
}


Complexity guarantees
Invariants
Models
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
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