InstanceOf

[Jacob Carlborg]

On 2013-06-23 13:26, Lemonfiend wrote:
>> foreach (I i; array) {
>>     if (B b = cast(B) i) { ... }
>> }
>
> Thanks all 3 of you for the quick and identical answers. :)
>
> It had not occurred to me to use a cast for this, but indeed the
> language ref says the same:
> "In order to determine if an object o is an instance of a class B use a
> cast"
>
> It does a bit inelegant to me.. Or are casts simply extremely cheap?

You can do something like this as well:

if (i.classinfo is B.classinfo) { }

But doing the cast is more efficient if you want to use the object of as 
the type you're checking for.

You can also hide the cast in a function if you want to be a bit more 
clear of the intent:

T instanceOf (T) (Object value)
{
     return cast(T) value);
}

if (i.instanceOf!(B)) { }

-- 
/Jacob Carlborg