Collection constructors

A collection constructor is a system-defined function with the same name as the collection type. It returns a collection of the specified type.

The syntax for calling a constructor is as follows:

collection_type ( [ value [, value ]... ] )

In this syntax, collection_type is the name of a previously declared nested table or varray type (not an associative array type). value is a valid value of the collection_type element. If collection_type is a varray type, the number of values cannot exceed the maximum value. If collection_type is a nested table type, there is no maximum value.

If the parameter list is empty, the constructor returns an empty collection. Otherwise, the constructor returns a collection containing the specified values.

You can assign the returned collection to a collection variable of the same type in a variable declaration or in the executable part of a block.

Example: Initialize a collection variable to an empty value.

obclient> DECLARE
  TYPE players IS VARRAY(5) OF VARCHAR2(20);
  team PLAYERS := players();   -- Initialize to an empty value

  PROCEDURE print_team (heading VARCHAR2) IS
  BEGIN
    DBMS_OUTPUT.PUT_LINE(heading);
    IF team.COUNT = 0 THEN
      DBMS_OUTPUT.PUT_LINE('Empty');
    ELSE
      FOR i IN 1..5 LOOP
        DBMS_OUTPUT.PUT_LINE(i || '.' || team(i));
      END LOOP;
    END IF;
    DBMS_OUTPUT.PUT_LINE('---');
  END;

BEGIN
  print_team('Team Members:');
  team := players('Charles', 'Carl', 'James', 'Gary','Brian');
  print_team('Team Members:');
END;
/
Query OK, 0 rows affected

Team Members:
Empty
---
Team Members:
1.Charles
2.Carl
3.James
4.Gary
5.Brian
---

In the preceding example, the constructor is called twice: first to initialize the varray variable team to an empty value, and then in the executable part of the block to assign it a new value. The print_team stored procedure displays the initial and final values of team. The print_team procedure uses the collection method COUNT to determine whether team is empty.