🚀 go-pugleaf

In article <01BAEFD6.AD7E8620@dino.int.com> Eugene Lazutkin
<eugene@int.com> writes:

|> 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.

|> 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?

And just when I thought I'd found a solution to the auto_ptr
problem:-).

In fact, this is a weakness in the STL definition (IMHO).  STL
containers require *real* copy constructors, that actually copy.  For
something like auto_ptr, this is not reasonable.  Even supposing that
STL and the language could handle it, what would be the meaning of:

	vector< auto_ptr< T > >
	                    v( 10 , auto_ptr< T >( new T ) ) ;

Certainly not what it would seem to be.

A possible solution would be to have two functions everywhere where
the STL requires a fill object.  (The current version has one
function, with a default parameter T() as fill.)  The version without
the fill object parameter would use the default constructor, rather
than copy.  Obviously, this is only interesting if the implementation
only instantiates functions that are actually used.  (I believe that
this is supposed to be the case, although I know that many
implementations do not do this.)

This still leaves a problem with the internal functions, such as
reserve, which may copy the data.  While not a problem for auto_ptr
(since they are copying non-const lvalues), it may be a problem for
other classes.
--
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
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