Display Form {R}←⎕DF Y

⎕DF sets the Display Form of a namespace, a GUI object, a Class, or an Instance of a Class.

Y must be ⎕NULL or a simple character array that specifies the display form of a namespace. If defined, this array will be returned by the format functions and ⎕FMT instead of the default for the object in question. This also applies to the string that is displayed when the name is referenced but not assigned (the default display). If Y is ⎕NULL, ⎕DF resets the Display Form to the default.

The result R is the previous value of the Display Form which initially is ⎕NULL.

Example

      'F'⎕WC'Form'
      ⍕F
#.F
      ⍴⍕F
3
      ⎕FMT F
#.F
      ⍴⎕FMT F
1 3
      F ⍝ default display uses ⍕
#.F

      F.⎕DF 'Pete''s Form'
      ⍕F
Pete's Form
      ⍴⍕F
11
      ⎕FMT F
Pete's Form
      ⍴⎕FMT F
1 11

Notice that ⎕DF will accept any character array, but ⎕FMT always returns a matrix.

      F.⎕DF 2 2 5⍴⎕A
      F
ABCDE
FGHIJ

KLMNO
PQRST
      ⍴⍕F
2 2 5

      ⍴⎕←⎕FMT F
ABCDE
FGHIJ

KLMNO
PQRST
5 5

Note that ⎕DF defines the Display Form statically, rather than dynamically.

      'F'⎕WC'Form' 'This is the Caption'
      F
#.F

      F.(⎕DF Caption)⍝ set display form to current caption
      F
This is the Caption

      F.Caption←'New Caption' ⍝ changing caption does not
                              ⍝ change the display form
      F
This is the Caption

You may use the Constructor function to assign the Display Form to an Instance of a Class. For example:

:Class MyClass
    ∇ Make arg
      :Access Public
      :Implements Constructor
      ⎕DF arg
    ∇
:EndClass ⍝ MyClass

      PD←⎕NEW MyClass 'Pete'
      PD
Pete

It is possible to set the Display Form for the Root and for ⎕SE

      )CLEAR
clear ws
      #
#
      ⎕DF ⎕WSID
      #
CLEAR WS

      ⎕SE
⎕SE
      ⎕SE.⎕DF 'Session'
      ⎕SE
Session

Note that ⎕DF applies directly to the object in question and is not automatically applied in a hierarchical fashion.

      'X'⎕NS ''
      X
#.X

      'Y'X.⎕NS ''
      X.Y
#.X.Y
      X.⎕DF 'This is X'
      X
This is X

      X.Y
#.X.Y