double const declarations

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3 total messages Started by dak Mon, 25 Mar 1996 18:09

#3800

Author: dak
Date: Mon, 25 Mar 1996 18:09

25 lines
1544 bytes

I've just encountered a problem in one of our template design and wondered
what could be done about it. It concerns const reference return value from
a templated member function, for example:

template <class T> class SmartPtr
{
	// ... whatever:
public:
	const T & Dereference ();
};

The problem arise when T is instantiated with a Container of constants:

SmartPtr<const int> a;

Here we have a double const which is not supported by the compiler, nor the
standard, I believe.  Is there a fix or should we abandon all hope of using
const returns in templates ?
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Re: double const declarations

#3810

Author: James Kanze US/ESC 60/3/141 #407...
Date: Tue, 26 Mar 1996 16:23

40 lines
2273 bytes

In article <Pine.A32.3.91.960325093715.29874A-100000@zorglub.cae.ca>
dak <pierreba@poster.cae.ca> writes:

|> I've just encountered a problem in one of our template design and wondered
|> what could be done about it. It concerns const reference return value from
|> a templated member function, for example:

|> template <class T> class SmartPtr
|> {
|> 	// ... whatever:
|> public:
|> 	const T & Dereference ();
|> };

|> The problem arise when T is instantiated with a Container of constants:

|> SmartPtr<const int> a;

|> Here we have a double const which is not supported by the compiler, nor the
|> standard, I believe.  Is there a fix or should we abandon all hope of using
|> const returns in templates ?

The draft standard forbids two explicit const's.  If the duplicate
Const result from typedef's, etc., it's OK.  (I don't know if the
actual words mention template instantiation types, but if they don't
I'm sure that it is an editorial oversight, and not the intent.)

--
James Kanze         Tel.: (+33) 88 14 49 00        email: kanze@gabi-soft.fr
GABI Software, Sarl., 8 rue des Francs-Bourgeois, F-67000 Strasbourg, France
Conseils, études et réalisations en logiciel orienté objet --
                -- A la recherche d'une activité dans une region francophone



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Re: double const declarations

#3858

Author: David Byrden
Date: Thu, 28 Mar 1996 21:16

24 lines
1597 bytes

dak <pierreba@poster.cae.ca> wrote:

>The problem arise when T is instantiated with a Container of constants:
>
>SmartPtr<const int> a;
>
>Here we have a double const which is not supported by the compiler, nor the
>standard, I believe.  Is there a fix or should we abandon all hope of using
>const returns in templates ?


     Sheer common sense tell you that we have to allow this. It can arise 
with 'volatile' as well. The Microsoft compiler gives just a warning.

                                       David




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