On Mar 21, 11 16:17, Don wrote:
Daniel Gibson wrote:
Am 21.03.2011 00:55, schrieb bearophile:
Among the things I've listed about Archetype there's one interesting
thing. Class instances aren't PODs, but sometimes I prefer reference
semantics and to populate fields in a plain way, expecially for
simple classes.
Time ago I and other people have suggested a syntax like (this also
to avoid a class of bugs
http://d.puremagic.com/issues/show_bug.cgi?id=3878 ):
class Foo {
string x;
int y = 1;
this(this.x, this.y) {}
}
void main() {
Foo f3 = new Foo("hello", 10);
}
Yeah, I still like that idea ;)
A simpler solution are classes with automatic constructors:
class Foo {
string x;
int y = 1;
}
void main() {
Foo f1 = new Foo(); // Good
Foo f2 = new Foo("hello"); // Good
Foo f3 = new Foo("hello", 10); // Good
}
What kind of problems are caused by this? :-)
You'd have to know the order in that the members are defined in the
class (and you may not change the order).
Just imagine
class Foo {
int bla;
int baz;
}
new Foo(42, 3); // what is bla, what is baz?
and then you decide "uh I'd prefer to have my class members ordered
alphabetically" and *bamm* all you code silently breaks.
having a this(this.bla, this.baz) {} would clearly document which
argument in the constructor belongs to which class member and the
class members ordering wouldn't matter.
Cheers,
- Daniel
I agree. But unfortunately, the idea is a relatively complicated feature
with a lot of special cases. For example, this(this.bla, this.bla){}
'int f(int x, int x) {}' is a syntax error. So should 'this(this.x,
this.x){}'.
and what if the class contains a union and you set multiple members of it?
The whole thing is actually quite messy. It's not _terrible_, but it's
far from trivial, and it's more complicated than some far more powerful
and useful language features.
The syntax
this(args, this.x.y.z, args, this.p.q.r = s, arg = t)
{
statements;
}
could just lower to
this(args, typeof(this.x.y.z) z, args, typeof(this.p.q.r) r = s,
arg = t)
{
this.x.y.z = z;
this.p.q.r = r;
statements;
}
Would this be too complicated?
(Not that I like this idea... But I think it is not really that messy)
