On Wednesday, 26 June 2013 at 04:16:30 UTC, Ali Çehreli wrote:
On 06/25/2013 09:05 PM, Jonathan M Davis wrote:
> On Wednesday, June 26, 2013 05:35:03 cal wrote:
>> On Wednesday, 26 June 2013 at 02:50:51 UTC, Eric wrote:
>>> Is there a way to overload the ! operator? I can't seem to
get
>>> it to work with the standard unaryOp method. I need this
>>> because
>>> I am making a wrapper for a C++ API that has ! overloaded.
>>>
>>> -Eric
>>
>> According to http://dlang.org/operatoroverloading.html#Cast,
the
>> following are rewritten:
>>
>> if (e) => if (e.opCast!(bool))
>> if (!e) => if (!e.opCast!(bool))
>>
>> So perhaps you need to override opCast!(bool).
>
> 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).
Works for ternary as well.
The other option is 'alias this' but it is a little dangerous
because bool is an arithmetic type. So, opCast would be better.
import std.stdio;
struct S
{
int i;
bool truth() const
{
return i == 42;
}
alias truth this;
}
void foo(bool b)
{
writeln(b);
}
void main()
{
auto s = S(42);
if (s){
}
while (s) {
break;
}
int i = s ? 4 : 5;
foo(s);
// What does it mean?
writeln(s + 2);
writeln(!s - 7);
}
> So, if you need to be able to do !obj in the general case,
that's not going to
> work
It surprisingly works both with opCast and 'alias this'.
Ali
Thanks for all the insignt. But I think I'm just going to fudge
this one
with a "bang()" method...
Incidently, for this project I figured out an interesting use of
alias.
The C++ classes I am wrapping have a lot of virtual methods with
all primitive arguments. So I create an D-interface for them,
and wrap the rest with C methods. The wrapper class then makes
methods that call the C methods, and then aliases the interface
reference to "this" so that the wrapper class instance points to
both the C++ native methods as well as the C-wrapped methods.
-Eric
