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digitalmars.D.learn - Runtime class check

reply funog <funog ifrance.com> writes:
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 ^^)
Apr 20 2007
parent reply BCS <BCS pathlink.com> writes:
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
}
Apr 20 2007
parent reply funog <funog ifrance.com> writes:
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" ;)
Apr 20 2007
parent reply Chris Nicholson-Sauls <ibisbasenji gmail.com> writes:
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
Apr 20 2007
parent Daniel Keep <daniel.keep.lists gmail.com> writes:
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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Apr 20 2007