Procedure Overloading

Procedure Overloading

OVERLOAD declares one procedure name that calls one of several candidate procedures, chosen by the arguments at each call. rpgc follows IBM i's rules.

Declaration

DCL-PR fmtNum VARCHAR(40);
  n PACKED(15:2) VALUE;
END-PR;

DCL-PR fmtText VARCHAR(40);
  s VARCHAR(30) CONST;
END-PR;

DCL-PR format VARCHAR(40) OVERLOAD(fmtNum : fmtText);

• The overloaded prototype is one statement: it has no parameters, so no END-PR (RNF3551).
• Every candidate returns the overloaded prototype's type — here VARCHAR(40) (RNF3244).

Calling

A call goes to the one candidate its arguments fit:

• the number of arguments must be one the candidate takes (OPTIONS(*NOPASS) makes trailing parameters optional);
• a VALUE or CONST parameter takes any argument of its type family — a number for any numeric type, a string for CHAR or VARCHAR, a date for a DATE;
• a parameter passed by reference takes only a variable of exactly its type.

If no candidate fits, the call is an error (RNF3245); so is a call that more than one fits (RNF3246). rpgc does not pick the closest match. An INT(10) candidate and a FLOAT(8) one, both by VALUE, both fit abs(-7), so that pair cannot be overloaded. Make candidates differ in type family or in number of parameters instead.

format(42);        // a number: fmtNum
format('hello');   // a string: fmtText

Full Example

**FREE

CTL-OPT MAIN(main);

DCL-PR fmtNum VARCHAR(40);
  n PACKED(15:2) VALUE;
END-PR;

DCL-PR fmtDate VARCHAR(40);
  d DATE VALUE;
END-PR;

DCL-PR fmtText VARCHAR(40);
  s VARCHAR(30) CONST;
END-PR;

DCL-PR square INT(10);
  side INT(10) VALUE;
END-PR;

DCL-PR rectangle INT(10);
  width INT(10) VALUE;
  height INT(10) VALUE;
END-PR;

// An overloaded prototype is one statement: no parameters, no END-PR
DCL-PR format VARCHAR(40) OVERLOAD(fmtNum : fmtDate : fmtText);
DCL-PR area INT(10) OVERLOAD(square : rectangle);

DCL-PROC main;
  DCL-PI *N;
  END-PI;

  DCL-S count INT(10) INZ(42);
  DCL-S due DATE;

  due = %DATE('2024-01-15');

  DSPLY format(count);         // a number: fmtNum
  DSPLY format(3.5);           // any numeric type: fmtNum
  DSPLY format(due);           // a date: fmtDate
  DSPLY format('hello');       // a string: fmtText

  DSPLY %CHAR(area(4));        // one argument: square
  DSPLY %CHAR(area(3 : 5));    // two: rectangle
END-PROC;

DCL-PROC fmtNum;
  DCL-PI *N VARCHAR(40);
    n PACKED(15:2) VALUE;
  END-PI;
  RETURN 'number ' + %CHAR(n);
END-PROC;

DCL-PROC fmtDate;
  DCL-PI *N VARCHAR(40);
    d DATE VALUE;
  END-PI;
  RETURN 'date ' + %CHAR(d);
END-PROC;

DCL-PROC fmtText;
  DCL-PI *N VARCHAR(40);
    s VARCHAR(30) CONST;
  END-PI;
  RETURN 'text ' + s;
END-PROC;

DCL-PROC square;
  DCL-PI *N INT(10);
    side INT(10) VALUE;
  END-PI;
  RETURN side * side;
END-PROC;

DCL-PROC rectangle;
  DCL-PI *N INT(10);
    width INT(10) VALUE;
    height INT(10) VALUE;
  END-PI;
  RETURN width * height;
END-PROC;