_create

The optional _create function can be used for variable initialization.

The behaviour slightly differs depending on whether the function has parameters or not.

Note: This function cannot be called explicitly by name, it is used automatically.

Without parameters

The simplest form of _create does not take any parameters.

Such function is called automatically in case of:

declaration of a scalar variable of a given type

The typical use of _create without parameters is an assignment of the default element values:

TYPE PacMan
    R AS BYTE
    G AS BYTE
    B AS BYTE

    ' As we all now, PacMan is yellow by default :P
    FUNCTION _create()
        me.R = 255
        me.G = 255
        me.B = 0
    END FUNCTION
END TYPE

DIM player1 AS PacMan   ' player1 is yellow by default

DIM player2 AS PacMan   ' player2 is created yellow by default
player2.R = 0           ' ...but changed to green thanks to override below
player2.G = 255
player2.B = 0

Note: Should you create an array of given type, _create is not called at the moment.

With parameters

The advanced form of _create allows us advanced initialization.

For our case of Point2D it allows us to set x and y during the variable creation.

TYPE Point2D
  x AS SINGLE
  y AS SINGLE
  
  FUNCTION _create(x AS SINGLE, y AS SINGLE)
    ME.x = x
    ME.y = y
  END FUNCTION
END TYPE

DIM point AS Point2D(1, 2)

Now x contains 1 and y is equal to 2.

As you can see, the _create function is not explicitly called, but any parameters passed to your UDT upon creation are passed to _create automatically.

Without _create, you would need to initialize the variable the hard way:

DIM point AS Point2D
point.x = 1
point.y = 2

Note: It is still possible to declare Point2D as DIM point AS Point2D, without any parameters. In such a case _create is not called and x and y will both have a value of zero.