6.6 Overloading of Operators
1
{operator}
{user-defined operator}
{operator (user-defined)}
An
operator is a function whose
designator
is an
operator_symbol. [Operators, like other
functions, may be overloaded.]
Name Resolution Rules
2
Each use of a unary or binary operator is equivalent
to a function_call with function_prefix
being the corresponding operator_symbol, and
with (respectively) one or two positional actual parameters being the
operand(s) of the operator (in order).
2.a
To be honest: We also use the term operator
(in Section 4 and in
6.1) to refer to one of
the syntactic categories defined in
4.5, “
Operators
and Expression Evaluation” whose names end with “_operator:”
logical_operator,
relational_operator,
binary_adding_operator,
unary_adding_operator,
multiplying_operator, and
highest_precedence_operator.
Legality Rules
3
The subprogram_specification
of a unary or binary operator shall have one or two parameters, respectively.
A generic function instantiation whose designator
is an operator_symbol is only allowed if the
specification of the generic function has the corresponding number of
parameters.
4
Default_expressions are
not allowed for the parameters of an operator (whether the operator is
declared with an explicit subprogram_specification
or by a generic_instantiation).
5
An explicit declaration of "/=" shall not
have a result type of the predefined type Boolean.
Static Semantics
6
A declaration of "=" whose result type
is Boolean implicitly declares a declaration of "/=" that gives
the complementary result.
7
8 The operators "+" and "–"
are both unary and binary operators, and hence may be overloaded with
both one- and two-parameter functions.
Examples
8
Examples of user-defined
operators:
9
function "+" (Left, Right : Matrix) return Matrix;
function "+" (Left, Right : Vector) return Vector;
-- assuming that A, B, and C are of the type Vector
-- the following two statements are equivalent:
A := B + C;
A := "+"(B, C);
Extensions to Ada 83
9.a
{
extensions to Ada 83}
Explicit
declarations of "=" are now permitted for any combination of
parameter and result types.
9.b
Explicit declarations of "/=" are
now permitted, so long as the result type is not Boolean.
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