🚀 go-pugleaf

ark@research.att.com (Andrew Koenig) writes:

>In article <MATT.95Sep23125440@Austern>
>martelli@cadlab.cadlab.it (Alex Martelli) writes:

>> avoiding the template author the chore of thinking up a dummy type
>> name in this situation...?  Or am I missing something here...?

>You're missing something.

>	template<class T> class X {
>		int a;
>		void f() {
>			T::Pointer (a);		// *
>		}
>	};

>If T::Pointer is the name of a type, the line with the comment
>declares a local variable inside function f that is of type T::Pointer.
>If, on the other hand, T::Pointer is the name of a function, then
>the line with the comment calls that function passing it the
>member names `a' of class X.

So far, so clear.

>This shows that in general it is necessary for the compiler to know
>whether each identifier is the name of a type.  In the case of members
>of template parameters, there's no easy way to know that in advance,
>so the "typename" keyword provides a way to say.

And if typename is absent, then T::Pointer will be taken for not
a typename, right?

So, what would be wrong with the idiom I suggested could have been
used instead -- if T::Pointer is used as in your example, take it
as not a typename; if you need to use a type name qualified by a
template parameter class, you would then have to write:

	void f() {
	    typedef T::Pointer anyoldname;
	    anyoldname a;
	}

This _is_ unambiguous, isn't it?  T::Pointer _must_ be a type name
in this usage -- unless I'm missing something here, which I think
you still have not shown.

Is typename just syntactic sugar for something that could have been
obtained with a not-particularly-obscure idiom for this situation?
That's what I was asking when I asked "what happened to minimalism".
I guess there must be some reason to make the typedef-idiom substitute
for "typename" not workable or not desirable, but, what IS it?


Alex
--
DISCLAIMER: these are TOTALLY personal opinions and viewpoints, NOT connected
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Email: martelli@cadlab.it                            Phone: +39 (51) 597313
CAD.LAB s.p.a., v. Ronzani 7/29, Casalecchio, Italia   Fax: +39 (51) 597120

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