Gforth Manual
5.21.3.7 Method conveniences
In a method you usually access the receiving object pretty often. If
you define the method as a plain colon definition (e.g., with
:noname), you may have to do a lot of stack
gymnastics. To avoid this, you can define the method with m:
... ;m. E.g., you could define the method for
drawing a circle with
| | m: ( x y circle -- )
( x y ) this circle-radius @ draw-circle ;m
|
When this method is executed, the receiver object is removed from the
stack; you can access it with this (admittedly, in this
example the use of m: ... ;m offers no advantage). Note
that I specify the stack effect for the whole method (i.e. including
the receiver object), not just for the code between m:
and ;m. You cannot use exit in
m:...;m; instead, use
exitm.(33)
You will frequently use sequences of the form this
field (in the example above: this
circle-radius). If you use the field only in this way, you can
define it with inst-var and eliminate the
this before the field name. E.g., the circle
class above could also be defined with:
| | graphical class
cell% inst-var radius
m: ( x y circle -- )
radius @ draw-circle ;m
overrides draw
m: ( n-radius circle -- )
radius ! ;m
overrides construct
end-class circle
|
radius can only be used in circle and its
descendent classes and inside m:...;m.
You can also define fields with inst-value, which is
to inst-var what value is to
variable. You can change the value of such a field with
[to-inst]. E.g., we could also define the class
circle like this:
| | graphical class
inst-value radius
m: ( x y circle -- )
radius draw-circle ;m
overrides draw
m: ( n-radius circle -- )
[to-inst] radius ;m
overrides construct
end-class circle
|
