Jarrett Billingsley Wrote:

> I perform downcasts extremely rarely.
That's *exactly* why you need safe cast.

> 
> if(auto y = cast(Y)x)
>     ...
> else
>     // not a Y, try something else
yeah, try something else, hide the bug :)

> Furthermore, it's a lot easier and more efficient to have the cast return null and throw an exception _only if needed_ than to throw an exception and then have to catch it:

most programmers won't bother to thow an exception in this case, they just cast and go.

> For that matter, some languages (like C#) have both kinds of casts - one that throws an exception and one that doesn't.  Either can really be implemented in the other, but the null-returning kind is more basic and efficient.
...efficient bugmaker.

terranium wrote:
> Jarrett Billingsley Wrote:
> 
> 
>>I perform downcasts extremely rarely.
> 
> That's *exactly* why you need safe cast.
> 

How does that follow? I don't see the connection.

> 
>>if(auto y = cast(Y)x)
>>    ...
>>else
>>    // not a Y, try something else
> 
> yeah, try something else, hide the bug :)
> 

That's not a bug. That is the normal idiom for checking to see if x is a Y and acting on it.

> 
>>Furthermore, it's a lot easier and more efficient to have the cast return null and throw an exception _only if needed_ than to throw an exception and then have to catch it:
> 
> 
> most programmers won't bother to thow an exception in this case, they just cast and go.
> 

And this will result in a Seg-V. The program will stop in a predictable manner. IMHO (and it seems others opinions) that is what matters.

> 
>>For that matter, some languages (like C#) have both kinds of casts - one that throws an exception and one that doesn't.  Either can really be implemented in the other, but the null-returning kind is more basic and efficient. 
> 
> ...efficient bugmaker.

the same can be said going the other way. IMHO any code that take a

> the same can be said going the other way. 

dang non-linear editing (scratch the following):

> IMHO any code that take a

"terranium" <spam@here.lot> wrote in message news:fvs67v$1gge$1@digitalmars.com...

> That's *exactly* why you need safe cast.
> ...
> yeah, try something else, hide the bug :)
> ...
> ...efficient bugmaker.

I _really_ don't understand where you're coming from here.  I'd be interested to see some example of code where an invalid downcast were a bug and where a failed cast _should_ throw an exception.  I've only ever used downcasts in D as a replacement for Java's "instanceof", where it's just a simple typecheck.

Jarrett Billingsley Wrote:

> > yeah, try something else, hide the bug :)
> > ...
> > ...efficient bugmaker.
> 
> I _really_ don't understand where you're coming from here.  I'd be interested to see some example of code where an invalid downcast were a bug and where a failed cast _should_ throw an exception.  I've only ever used downcasts in D as a replacement for Java's "instanceof", where it's just a simple typecheck.

void GetNodes()
{
 auto obj = Parser.GetNextObject();
 MyList.Add(cast(INode)obj);
}

Reply to terranium,

> Jarrett Billingsley Wrote:
> 
>>> yeah, try something else, hide the bug :)
>>> ...
>>> ...efficient bugmaker.
>> I _really_ don't understand where you're coming from here.  I'd be
>> interested to see some example of code where an invalid downcast were
>> a bug and where a failed cast _should_ throw an exception.  I've only
>> ever used downcasts in D as a replacement for Java's "instanceof",
>> where it's just a simple typecheck.
>> 
> void GetNodes()
> {
> auto obj = Parser.GetNextObject();
> MyList.Add(cast(INode)obj);
> }

Dang, you just reminded me that I do have some code that downcasts and expects stuff to work (it check the cast though). It's in a generated parser I'm working on.