Dear All

Am currently writing some somewhat hairy template
code that involves me deriving from a class type that
is buried deep within a load of templated and typedef'd
code. And therein lies the problem. I want to use
a typedef to simplify my base class type e.g. I want
to write

typedef my_incredibly_long_type_name short_name;

class derived : public short_name
{...};

rather than

class derived : public my_incredibly_long_type_name
{...};

(In reality the long name is even longer and I
use it elsewhere making the typedef more beneficial
than in this cut down example.)

However para 7.1.3/4 of the standard says:

"A typedef-name that names a class is a class-name (9.1).
If a typedef-name is used following the class-key
in an elaborated-type-specifier (7.1.5.3) or in the
class-head of a class declaration...the program is ill-formed."
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

The class-head includes the part that specifies
base classes. Therefore I am prevented from
using my typedef name there.

Is my interpretation of the standard correct? If so,
what is the rationale behind this decision?

It seems bizarre; after all, I can quite happily use
my typedef name to declare a data member. And
what is a base class in reality but a data member
with a bit of extra compiler magic thrown in?

Kind regards

Garry Lancaster
Codemill Ltd
Visit our web site at http://www.codemill.net

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"Garry Lancaster" <glancaster@ntlworld.com> writes:
> However para 7.1.3/4 of the standard says:
>
> "A typedef-name that names a class is a class-name (9.1).
> If a typedef-name is used following the class-key
> in an elaborated-type-specifier (7.1.5.3) or in the
> class-head of a class declaration...the program is ill-formed."
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

I would parse this paragraph as

"If a typedef-name is used
 following the class-key in an elaborated-type-specifier (7.1.5.3)
 or
 following the class-key in the class-head of a class declaration (9)
 [...] the program is ill-formed."

Is this worth a defect report for unclear language?
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Garry Lancaster:
> > However para 7.1.3/4 of the standard says:
> >
> > "A typedef-name that names a class is a class-name (9.1).
> > If a typedef-name is used following the class-key
> > in an elaborated-type-specifier (7.1.5.3) or in the
> > class-head of a class declaration...the program is ill-formed."
> > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Jens Kilian:
> I would parse this paragraph as
>
> "If a typedef-name is used
>  following the class-key in an elaborated-type-specifier (7.1.5.3)
>  or
>  following the class-key in the class-head of a class declaration (9)
>  [...] the program is ill-formed."

Of course! Thanks, that makes a lot more sense.

> Is this worth a defect report for unclear language?

I'm not sure.

Kind regards

Garry Lancaster
Codemill Ltd
Visit our web site at http://www.codemill.net

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