On Wednesday, 26 June 2013 at 05:08:07 UTC, Jonathan M Davis
wrote:
On Wednesday, June 26, 2013 06:59:14 cal wrote:
On Wednesday, 26 June 2013 at 04:06:05 UTC, Jonathan M Davis
wrote:
> Yeah, that should work for the conditions in if, while, and
> for
> loops but
> won't work for anything else (_maybe_ ternary operators, but
> I'm not sure).
> So, if you need to be able to do !obj in the general case,
> that's not going to
> work
...
import std.stdio;
struct S {
int x;
bool opCast(T)() if (is(T == bool)) {
return x == 0;
}
}
void main() {
auto s = S(1);
auto b = !s;
writeln(b); // true
}
Is this not supposed to work?
No, it's not. That would require an implicit cast (which
requires using alias
this). opCast gives you an explicit cast only. Where that
becomes confusing is
the fact that the compiler inserts explicitly casts to bool in
conditions for
if statements, loops, and the ternary operator. e.g.
if(foo) {...}
becomes
if(cast(bool)foo) {...}
So, if you've overloaded opCast to bool, then it'll get used in
the conditions
for if statements, loops, and the ternary operator. But no
explicit cast is
added just for putting ! in front of a variable. It works with
something like
if(!foo) {...}
simply because that becomes
if(!cast(bool)foo) {...}
But nothing special is done for !, and !a will not call opCast.
- Jonathan M Davis
But that code I posted does work, and gives the output shown. Am
I misunderstanding?
