using a typedefed variable with library classes

[Charles Hixson]

bearophile wrote:
> Bill Baxter:
> 
>> The first time I tried to use it my thought was to do
>>   typedef Exception MyException;
>> To create a different exception type.  That doesn't work so I kinda
>> just said, eh whatever, this typedef stuff doesn't work yet.
> 
> You are right, typedef was invented before classes and OOP, so what you say doesn't work :-)
> But I think typedef may be modified to work as you want too, that is to define a subtype (so the runtime typeinfo of MyException too has to be different!). I/we can ask Walter what he thinks about this.
> 
> 
>> Now I can't accidentally assign a vertex handle to a face handle.
>> That could be useful.
> 
> Right. But so far I don't see problems in extending the semantics of typedef to work with OOP too. Maybe other people here can spot a problem. I presume Walter doesn't read this newsgroup, so I can post a summary in the main D group too, later.
> 
> Bye,
> bearophile
Well, my use case just involves being able to use library function with 
the proper base type.  (I.e., int instead of long or byte when I do
typedef int LocalType;
LocalType t;
File f;
f.write(t);

I'll grant that I *can* use alias for such a purpose, but that doesn't 
distinguish between LocalType and ArrayIndex in routines defined for 
those types.  E.g.:
typedef  int ArrayIndex;
void zeroIndex(out ArrayIndex ai)  {	ai = 0;  }
zeroIndex(t);

Should throw an error.  If I'm using alias it doesn't (and shouldn't);