Global Packages Versus Local Packages

The scope of a package instance makes a difference. Package instances that are created in the global scope typically are created and deleted (allocated and freed) once and used over and over again. Package instances that are created in a local scope are created and deleted each time the scope is entered and exited. For example, a package instance that is created in a method's scope is created and deleted each time a method is called. The creation and deletion time can be costly for some packages.

The following examples use the hash package. This technique can be used for all packages.

This example creates a hash package instance that is global, created and deleted with the package instance, and reused between calls to load_and_clear.

/** FAST **/
package mypack;
  dcl double k d;
  dcl package hash h([k], [d]);
 
  method load_and_clear();
    dcl double i;
    do k = 1 to 100;
      d = 2*k;
      h.add();
    end;
    h.clear();
  end;
endpackage;

This example creates a hash package instance that is local to the method and created and deleted for each call to load_and_clear.

/** SLOW **/
package mypack;
  dcl double k d;
 
  method load_and_clear();
    dcl package hash h([k], [d]);
    dcl double i;
    do k = 1 to 100;
      d = 2*k;
      h.add();
    end;
    h.clear();
  end;
endpackage;