Referencing entities in descendants

When you declare a variable whose data type is a kind of object,
such as a window, you can use the variable to reference any entity
defined in the object, but not in one of its descendants. Consider
the following code:

Mycust is declared as a variable of type w_customer
(mycust is a w_customer window). If w_customer
contains a StaticText control named st_name, then the last
statement shown above is legal.

However, consider the following case:

Here, newwin is defined as a variable of type window. PowerBuilder rejects
the above code because the compiler uses what is called strong
type checking: the PowerBuilder compiler does not allow
you to reference any entity for an object that is not explicitly
part of the variable’s compile-time
data
type.

Because objects of type window do not contain a st_name
control, the statement is not allowed. You would need to do one
of the following:

• Change the declaration of
  newwin to be a w_customer (or an ancestor window that also
  contains a st_name control), such as:
  PowerBuilder

  w_customer newwin

  1	w_customer newwin

  PowerBuilder

  string winname = "w_customer"

  1	string winname = "w_customer"

  1

  PowerBuilder

  Open(newwin, winname)

  1	Open(newwin, winname)

  PowerBuilder

  // Legal now

  1	// Legal now

  PowerBuilder

  newwin.st_name.text = "Joe"

  1	newwin.st_name.text = "Joe"

• Define another variable, of type w_customer,
  and assign it to newwin, such as:
  PowerBuilder

  window newwin

  1	window newwin

  PowerBuilder

  w_customer custwin

  1	w_customer custwin

  PowerBuilder

  stringwinname = "w_customer"

  1	stringwinname = "w_customer"

  1

  PowerBuilder

  Open(newwin, winname)

  1	Open(newwin, winname)

  PowerBuilder

  custwin = newwin

  1	custwin = newwin

  PowerBuilder

  // Legal now

  1	// Legal now

  PowerBuilder

  custwin.st_name.text = "Joe"

  1	custwin.st_name.text = "Joe"

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