15.7 Logical operators

Logical operators and, or, xor and not can be overloaded. These operators are normally used on simple types in two different ways:

1. As boolean operators, in which case the result is a boolean (except for not)

2. As bitwise operators, in which case the result is an ordinal type.

When overloading these operators, the result type is not restricted. This means you can define the operators as boolean logic operators:

Type
  Rec = record
    a,b : Boolean;
  end;

Operator and (r1,r2 : Rec) z : boolean;

begin
  z:=(R1.a and R2.a) or (R1.b and r2.b);
end;

Operator or (r1,r2 : Rec) z : Boolean;

begin
  z:=(R1.a or R2.a) and (R1.b or r2.b)
end;

Operator xor (r1,r2 : Rec) z : Boolean;

begin
  z:=(R1.a xor R2.a) and (R1.b xor r2.b)
end;

Operator not (r1 : Rec) z : rec;

begin
  z.A:=not R1.a;
  z.B:=not R1.b;
end;


var
r1,r2 : Rec;

begin
  Writeln(r1 and r2);
  Writeln(r1 or r2);
  Writeln(r1 xor r2);
  Writeln((not r1).a);
end.

But it is also possible to have different return types:

Operator and (r1,r2 : Rec) z : string;

begin
  Str(Ord((R1.a and R2.a) or (R1.b and r2.b)),Z);
end;

The compiler will always check the return type to determine the final type of an expression, and assignments will be checked for type safety.