Magic type return

[Regan Heath]

On Tue, 17 Jul 2012 15:23:05 +0100, bearophile <bearophileHUGS at lycos.com>  
wrote:

> Andrea Fontana:
>
>> class Known
>> {
>>          void* data; // external data by c api
>>          int type;  // 0 for int, 1 for string, etc. ..
>> }
>>
>> How can I implement a method like this?
>>
>> Known  known;  // <-- suppose known.type == 1;
>> string s  = known.value(); // <-- automatic
>
> To do this Known.value() needs to return different types according to  
> the run-time value of Known.type. This is not possible in a statically  
> typed language... You need to find other solutions.

Unless we had overload based on return type, right?

e.g.

class Known
{
   string value()
   {
     if (type != 1)
       throw..;
     return cast(string)data;
   }

   int value()
   {
     if (type != 0)
       throw ..;
     return cast(int)data;
   }
}

The compiler could produce the correct code/call for the line

string s = known.value();

then, but it's not a feature we're likely to see any time soon.

R

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