opEquals footprint

[Erik Rasmussen]

xs0 wrote:
> Erik Rasmussen wrote:
> 
>> xs0 wrote:
>>
>>> int opEquals(Object)
>>>
>>> so it overrides the default implementation found in, you guessed it, 
>>> Object :) Same goes for opCmp, I think..
>>>
>>>
>>> xs0
>>
>>
>> So what's the best way to actually check the type in the 
>> opEquals/opCmp method?  Something like...
>>
>> class A
>> {
>>   int opEquals(Object o)
>>   {
>>     // check for null
>>     if(o is null)
>>       return false;
>>     // check type
>>     if(typeid(typeof(o)) != typeid(A))
>>       return false;
>>     // cast
>>     A that = cast(A) o;
>>     // actually check fields
>>     return this.a == that.a && this.b == that.b && ...;
>>   }
>> }
>>
>> Or is there a better way?  asserts?
>>
>> How do you hard-core D programmers usually do it?
>>
>> Cheers,
>> Erik
> 
> 
> Something like this should be ok:
> 
> // optional
> if (this is o)
>     return true;
> 
> if (A that = cast(A)o) { // checks for null, too
>     return this.a==that.a && ...
> } else {
>     return false;
> }
> 
> OTOH, if you want to return false for subclasses, your version seems 
> fine to me.
> 
> 
> xs0

No, I definitely don't want it to return false for subclasses!

That "failed cast returns null" trick is handy.  That's waaay better 
than all that typeid(typeof()) crap.  Thanks guys.

Erik