InstanceOf

[Lemonfiend]

On Sunday, 23 June 2013 at 15:15:16 UTC, Jacob Carlborg wrote:
> 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.

Using the .classinfo is what I looked at before asking here.
However, according to the specs:
".classinfo applied to an interface gives the information for the 
interface, not the class it might be an instance of."
So the i.classinfo and B.classinfo would be different?

> 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)) { }

This is indeed what I did :)