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Functional Constructors in Theme-D
I redesigned the constructors in Theme-D version 2.0.0, see [1].
The design is inspired by the OCaml object system.
Constructors are special procedures used to create instances (objects)
of classes. They are not defined like other procedures but
Theme-D creates them using the
construct statement in a
class and field initializers in a class. The translator-generated
default constructor is sufficient in many cases. For example, consider
the class <complex> defined in the standard library:
(define-class <complex> (attributes immutable equal-by-value) (inheritance-access hidden) (fields (re <real> public hidden) (im <real> public hidden)) (zero (make <complex> 0.0 0.0)))The translator-generated default constructor takes two real arguments and sets the first to the field re and the second to the field
im .
The programs (define-class <widget> (fields (str-id <string> public module))) (define-class <window> (superclass <widget>) (construct ((str-id1 <string>) (i-x11 <integer>) (i-y11 <integer>) (i-x21 <integer>) (i-y21 <integer>)) (str-id1)) (fields (i-x1 <integer> public module i-x11) (i-y1 <integer> public module i-y11) (i-x2 <integer> public module i-x21) (i-y2 <integer> public module i-y21) (i-width <integer> public module (+ (- i-x21 i-x11) 1)) (i-height <integer> public module (+ (- i-y21 i-y11) 1))))The constructor of class <window> passes the first argument
str-id1 to the constructor of its superclass
<widget> . The constructors also initialize the fields using their
arguments. Note that the field initializers may contain more complex
expressions than just copying an argument variable.
Here is the second example: (define-class <widget> (construct ((str-id1 <string>)) () (nonpure)) (fields (str-id <string> public module (begin (console-display "new widget: ") (console-display-line str-id1) str-id1)))) (define-class <window> (superclass <widget>) (construct ((str-id1 <string>) (i-x11 <integer>) (i-y11 <integer>) (i-x21 <integer>) (i-y21 <integer>)) (str-id1) (nonpure)) (fields (i-x1 <integer> public module i-x11) (i-y1 <integer> public module i-y11) (i-x2 <integer> public module i-x21) (i-y2 <integer> public module i-y21) (i-width <integer> public module (+ (- i-x21 i-x11) 1)) (i-height <integer> public module (+ (- i-y21 i-y11) 1))))Here we log the calls to the constructor of <widget> to the
console. Note that we have to declare the constructors as
nonpure if they have side effects.
[1] Theme-D Homepage By Tommi Höynälänmaa at 2020-03-08 16:58 | LtU Forum | previous forum topic | next forum topic | other blogs | 3657 reads
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