Why does this opCmp function not work

[Steven Schveighoffer]

On 9/23/20 7:28 AM, Simen Kjærås wrote:
> On Wednesday, 23 September 2020 at 11:19:15 UTC, Ruby The Roobster wrote:
>> bool opEquals(shape rhs)
>> {
>> return(rhs.volume == this.volume);
>> }
> 
> This is a wrong implementation of opEquals for a class. The 
> documentation mentions 
> (https://dlang.org/spec/operatoroverloading.html#equals):
> 
>> 4. If overridding Object.opEquals() for classes, the class member 
>> function signature should look like:
>>
>> class C
>> {
>>     override bool opEquals(Object o) { ... }
>> }
> 
> A correct implementation would be:
> 
> override bool opEquals(Object o) {
>      if (!cast(Shape)o) return false;
>      return (cast(Shape)o).volume == this.volume;
> }

Or, more D way:

if(auto other = cast(Shape)o) return other.volume == this.volume;
return false;

-Steve