🚀 go-pugleaf

On 	Monday, January 29, 1996 12:50 PM, 	fjh@munta.cs.mu.OZ.AU (Fergus Henderson) wrote:
> esap@cs.tut.fi (Pulkkinen Esa) writes:
> 
> >template <class T>
> >class type_dereferencer<T*>
> >{
> >public:
> >  typedef T base_type;
> >};
> [...]
> >And if typedef templates were allowed, you could use a slightly better
> >syntax:
> >
> >template <class T>
> >typedef type_dereferencer<T>::base_type type_dereference;

Don't forget another point: YOU CAN'T INHERIT CONSTRUCTORS.  In fact

1) class B : public A {};

and

2) typedef A B;

is not the same if you have non-default constructors in the class A. 
You have to put some constructors in a 1st example, like

class B : public A 
{
public:
	B( T1 x ) : A(x)	{}
	B( T2 x ) : A(x)	{}
	B( T1 x, T2 y ) : A(x,y)	{}
	/* ... other constructors ... */
	B() : A()	{}
	B( const A& a ) : A(a) {}
};

if you are going to emulate 2nd.  To me the typedef templates would solve 
this problem easily and effectifely.

> Can someone please remind me why we decided not to allow typedef templates?

Yeah, why?

> It certainly seems like a bad idea to force everyone to use this silly
> obfuscation for what is obviously a common need.

I wrote several wrappers like written above for my application which uses STL.
When I change the set of possible constructors of the base class I need
find all appropriate wrappers and correct them too.  I have to keep my code
up-to-date manually.

Why do I use wrappers?  Just small example: vector< auto_ptr< T > > 
(or list< auto_ptr< T > >).  I f you tried it, you'd discover that STL 
(I use ObjectSpace's implementation) uses copy-ctor with a const parameter 
and auto_ptr doesn't define it.  The same for a copy-op. Additionally  
my VC++ 4.0 tries to instantiate some unused methods (?) and of course doesn't 
find less-operator.  That's why I need wrappers.

BTW, how come that auto_ptr from Standard C++ Library is incompatible with
vector<>, list<> and other STL containers from the same source? Or maybe I
have incorrect implementation?

> Fergus Henderson             	WWW: http://www.cs.mu.oz.au/~fjh
> fjh@cs.mu.oz.au              	PGP: finger fjh@128.250.37.3

Thanks in advance


	
Eugene Lazutkin
eugene@int.com
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