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From: Max TenEyck Woodbury <mtew@cds.duke.edu>
Subject: Re: Suggestion: "typeof" keyword
Date: 1999/08/23
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Christopher Eltschka wrote:
> 
> "Siemel B. Naran" wrote:
> >
> > On 13 Aug 99 15:52:23 GMT, Lisa Lippincott
> >
> > >/* what type goes here? */
> > >MultiplyAdd( const A& a, const B& b, const C& c )
> > >  { return a * b + c; }
> >
> > In one of my posts I used this
> >    typeof(A*B+C) MultiplyAdd(...) { ... }
> 
> That's problematic:
> 
> class X {};
> class Y { Y operator*(); };
> X operator*(X, Y);
> Y operator*(X*, Y);
> 
> typeof(X**Y) a
> 
> Is a of type X or of type Y?
> (That is, is the first star the multiplication operator and the
> second one the dereference operator, or is the first one part of
> the type, making a pointer to X, and the second one the
> multiplication operator?)

You need a slightly different syntax to distinguish the use of an
expression from the use of a type, as sizeof does. Since typeof
is not needed in the direct type specification case, it can be used 
to get the type of function signatures. For example:

typedef typeof operator *(X,Y)  XY;  // = X
typedef typeof operator *(X*,Y) pXY; // = Y

mtew@cds.duke.edu
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