On Thu, May 11, 2017 at 07:46:24PM -0400, Steven Schveighoffer via
Digitalmars-d wrote:
[...]
> But this still doesn't mean that *all* bool conversions are value
> based. In at least the struct and class cases, more than just the bits
> are checked.
[...]
Wait, what? You can use a *struct* as a bool condition?!
I tried this:
import std.stdio;
struct S {}
void main() {
S s;
if (s) { writeln("WAT"); }
}
But the compiler (rightly) said:
test.d(5): Error: expression s of type S does not have a boolean value
Or were you talking about structs that define opCast!bool? (In which
case it's certainly intentional and doesn't pose a problem.)
I can see classes being usable in conditions, though, since they're
essentially pointers hiding behind an abstraction. Still, it doesn't
quite sit right with me. For example:
class C { }
class D { bool opCast(T : bool)() { return false; } }
void main() {
C c;
D d = new D;
if (!c) { ... } // OK, expected semantics
if (!d) { ... } // *** What happens here?
}
Whereas had the last two lines been written:
if (c is null) { ... }
if (d is null) { ... }
the intent would be much clearer. (And of course, d would be usable
without "is null" if you actually intended to invoke opCast!bool.)
T
--
In a world without fences, who needs Windows and Gates? -- Christian Surchi
