Runtime class check

[Daniel Keep]

Chris Nicholson-Sauls wrote:
> funog wrote:
>> BCS Wrote:
>>
>>> funog wrote:
>>>> Is there a way to have a runtime class check other than
>>>> if(cast(X)y)
>>>> ( It just does not look really "nice" to me ^^)
>>>>
>>> Unless you are not going to use it as the type you are checking for
>>> what's wrong with that (or this)
>>>
>>> if(auto x = cast(X) y)
>>> {
>>>   // use x
>>> }
>>
>> You are right, it's nice. But i guess it means the answer to my
>> question is "no" ;)
> 
> Not strictly speaking, but certainly nothing more elegant.  You could
> presumably, for example, compare the .classinfo referances -- if
> (y.classinfo is X.classinfo) -- but... ew.  :)
> 
> -- Chris Nicholson-Sauls

Amusing anecdote: when I first started using D, I was under the
impression that cast(T) would throw an exception if the cast couldn't be
done.  So, off I went to write an instanceof function.

A few days later, I had this hideous piece of code that went and walked
the object's inheritance tree to find out if it could be cast to the
given type.

Almost immediately after I finished, I read something on the NG that
pointed out that cast(T) simply returns null if the cast failed.
Fiddlesticks.

Morale of this story: read the docs before you go assuming things :3

	-- Daniel

-- 
int getRandomNumber()
{
    return 4; // chosen by fair dice roll.
              // guaranteed to be random.
}

http://xkcd.com/

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