Overloaded Operators

Operators are Overloaded

• 2.0 + 3.0
• 2 + 3

User Defined Overloaded Operators

• Users can define functions whose names are strings that are operators
• Example:

with ada.Integer_text_io; use ada.Integer_text_io;
procedure tryOp is
    function "+"(i: Integer; f: Float) return integer is
    begin
        return i + (Integer(f));
    end "+";
begin

    put("+"(2, 3.0));

    put(2 + 3.0);

end tryOp; 
    

• Functions that are operators can be used in prefix mode or infix mode


• Functions that are operators can be defined for any type (eg arrays, records)


See package standard for declarations of integer operators

What Operators Can be Overloaded

• What are the Ada operators
• abs and mod not or rem xor
• = /= < <= > >=
• + - * / ** &


• + and - can be defined as unary or binary (ie with one or two parameters), or both


• If a definition of "=" returns a boolean, then "/=" is implicitly defined (and cannot be redefined).


• "/=" can only be redefined if it returns a non-boolean


• Technically the following are NOT operators and can't be redefined:
• in, not in, and then, or else

Overloaded Operators and Packages

• It is very common for a package to contain type definitions


• It is also very common for a package to contain to define operators that operate on those types


• When a package redefines operators, those operators can be used as infix operators if client has a use statement for that package
• Ada 95 introduced a new statement (the use type statement) that allows clients to use infix operators, without making the procedures available without the qualified name.
• Example needed here:

Overloaded Operators and Other Langauges

• Java: No
• C++: Yes