Re: [OT] Re: C++ *for Git*

"Marco Costalba" [off-list ref] writes:

On 9/23/07, David Kastrup [off-list ref] wrote:

quoted

"Marco Costalba" [off-list ref] writes:

quoted

And BTW

template <typename T>

is the thing in C++ that more remembers me of opaque pointers and
their use in C, the difference is that the first is fully type
checked.

Not really.  The difference is that the first generates new (and
optimized) code for every type which is something you can only do
using macros in C.  Class programming is similar to opaque pointers
(in particular concerning the generated code) but templates are really
more like macros, as their instantiation generates specialized code,
not at all like the handling of opaque pointers.

Probably if I had written like this was more clear:

template <typename T>  int some_function(T* p);

Huh?  How is this supposed to support your point?  There is nothing
like an opaque pointer involved here.  The point of opaque pointers is
that they can stand for a variety of types, whereas each template
instantiation can only substitute a single type.

And regarding 'new' code for each type I would like to remember that
template instantations of different types can be removed by
compiler/linker when the instantations are the same (i.e. produce
the same binary instuctions), this could happen for function
templates that handle pointers, as example.

Hardly.  The type constraints/virtual function tables of any called
function depending on T will be different.  And if indeed nothing
depends on T at all inside of the template, it is pointless not to
declare it as void *p in the first place: the type of *p will never be
used then.

-- 
David Kastrup, Kriemhildstr. 15, 44793 Bochum