Assignable
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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
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A type that is a model of Assignable
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x, y
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Object of type X
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Definitions
Valid expressions
Name
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Expression
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Type requirements
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Return type
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Copy constructor
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X(x)
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X
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Copy constructor
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X x(y);
X x = y;
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Assignment
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x = y [1]
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X&
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Swap
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swap(x,y)
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void
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Expression semantics
Name
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Expression
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Precondition
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Semantics
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Postcondition
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Copy constructor
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X(x)
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X(x) is a copy of x [2]
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Copy constructor
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X(x)
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X(x) is a copy of x [2]
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Copy constructor
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X x(y);
X x = y;
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x is a copy of y [2]
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Assignment
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x = y [1]
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x is a copy of y [2]
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Swap
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swap(x,y)
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Equivalent to
{
X tmp = x;
x = y;
y = tmp;
}
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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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1999 Silicon Graphics, Inc. All Rights Reserved.
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