Calling Constructors:

The Calls to a constructor are allowed wherever the function calls are allowed. Similarly to the functions, a constructor is called as a section of an expression, as the illustration below is a shown:

DECLARE

r1 Rational := Rational(2, 3);

FUNCTION average (x Rational, y Rational) RETURN Rational IS

BEGIN

...

END;

BEGIN

r1 := average(Rational(3, 4), Rational(7, 11));

IF (Rational(5, 8) > r1) THEN

...

END IF;

END;

Whenever you pass a parameter to a constructor, the call assigns its initial value to the attributes of the object being instantiated. You should supply a parameter for every attribute as, dissimilar constants and variables, the attributes cannot have the default values. As the illustration shown below, the nth parameter assigns a value to the nth attribute:

DECLARE

r Rational;

BEGIN

r := Rational(5, 6); -- assign 5 to num, and 6 to den

-- now r is 5/6

The later illustration shows that you can call a constructor using the named notation rather than that of the positional notation:

BEGIN

r := Rational(den => 6, num => 5); -- assign 5 to num, and 6 to den