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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.�
NOTES
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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