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From: "Greg Brewer" <nospam.gregb@hal-pc.org>
Subject: Re: Suggestion: "typeof" keyword
Date: 1999/08/13
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<niklasb@my-deja.com> wrote in message news:7nt3vl$1oe$1@nnrp1.deja.com...
> Suppose I'm writing a template function and II is an unknown
> iterator type. How can I refer to the type one gets by
> dereferencing an II object?
>
> In many cases I could say II::value_type, but only if II is
> a class that contains a typedef for value_type. What if II is
> a simple pointer type? The use of the "typedef ... value_type"
> convention in the standard library only highlights the need
> for a more universal mechanism.
>
> I have in mind a keyword, typeof, which would yield the type
> of an expression. Like its cousin "sizeof," typeof would not
> actually evaluate anything at run-time.
>
> Does anyone else think such a keyword would be valuable? Or
> is this a solution in search of a problem? Following is a
> (somewhat contrived) example of how typeof might be used.

I think this typeof() function would be doublely useful if it could be used
with extra text.  Consider,  a case I had.  I had several structures defined
in pairs.  The first was the class I used through out my program and the
second was a record class that was used to move data to/from a database.
There was also operators defined for moving that data.  A template was ideal
for this operation.

Consider one case, class Traits and class Traits_Record;
template <class T>
int StoreInDatabase(T *t)
{
   // at this point, I needed a record.  No way to declare one.
   // perhaps typeof could be designed to handle the problem as follows
   typeof(*t)##_Record record; // resolves to Traits_Record record;
   record.StoreData(t);
   return record.Write();
}

Just a consideration,
Greg Brewer




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