bearophile wrote:
Ary Borenszweig:
I'm normally interested to enter the if branch if x is not null and it
has an interesting value. For example, if I implement a String class I
would implement it as not being empty. But I think the biggest problem
is making a different semantic for this to structs and classes. You'll
have programmers wondering why the if branch was entered even if my
class implemented opBool not to enter it. But time will tell.
A solution can be to disallow opCast!(bool) in classes. So when in your code
you convert a struct (that already defines opCast!(bool)) to a class, or when
you try to add opCast!(bool) to a class, the compiler gives you a nice
compilation error, and saves you from possible bugs.
A warning too can be better than nothing.
For opCast maybe it would be better to have some examples, like:
T opCast(T)() if (is(T == bool)) {
}
T opCast(T)() if (is(T == int)) {
}
(it's not very intuitive that I have to do that to implement opCast,
it's different from the other operator overloading that rely on strings)
This works:
import std.stdio: writeln;
struct Foo {
int len;
this(int x) {
this.len = x;
}
T opCast(T:bool)() {
return this.len != 0;
}
T opCast(T:int)() {
return this.len;
}
}
Cool! Much, much nicer. (that's why I think some examples would be fine
there)
