Template instantiation

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2 total messages Started by John E. Potter Sun, 17 Mar 1996 03:59

#3704

Author: John E. Potter
Date: Sun, 17 Mar 1996 03:59

40 lines
1888 bytes

I have only found one compiler which accepts the following.  The others
attempt to instantiate class N prior to completing class L.  As I read
DWP-14.3 [temp.inst], class N<int> should not be instantiated in the
following code.  It would be instantiated when some class L<int> function
used an N<int>.

template <class T> class N;
template <class T> class L {
	public :
		// ...
	private :
		N<T>* ptr;
	};
template <class T> class N {
	private :
		N (T, const L<T>&);
		L<T> next;  // error L<int> incomplete type, size unknown
		T data;
		friend class L<T>;
	};
int main () {
	L<int> l;
	}

Do I have one correct compiler that accepts it, several correct compilers
which reject it, or (I hope not) all correct compilers because it is not
specified?

If the latter, is there any standard way to make this portable.  I can
change ptr to a void* and reinterpret_castrate everything, but that is
not very pleasing.

Thanks,
John
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Re: Template instantiation

#3752

Author: Nathan Myers, http://www.cantrip...
Date: Thu, 21 Mar 1996 02:48

35 lines
2224 bytes

John E. Potter wrote:
> 
> I have only found one compiler which accepts the following.  The others
> attempt to instantiate class N prior to completing class L.  As I read
> DWP-14.3 [temp.inst], class N<int> should not be instantiated in the
> following code.  It would be instantiated when some class L<int> function
> used an N<int>.
> 
> template <class T> class N;
> template <class T> class L { N<T>* ptr; };
> template <class T> class N { L<T> next; };
> int main () { L<int> l; }
> 
> Do I have one correct compiler that accepts it, several correct compilers
> which reject it, or (I hope not) all correct compilers because it is not
> specified?

You have one (at least semi-) correct compiler, and several broken ones.

> If the latter, is there any standard way to make this portable?  I can
> change ptr to a void* and reinterpret_castrate everything, but that is
> not very pleasing.

You could change the member to a void* and provide an (inline) access 
function that does the cast, in only one place.  Better to use 
non-broken compilers, of course.

Nathan Myers
ncm@cantrip.org  http://www.cantrip.org/
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