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From: philh@vision25.demon.co.uk (Phil Hunt)
Subject: Re: GPL and "free" software
Date: 1999/05/02
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Date: 1999-05-02T00:00:00+00:00
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In article <372C1824.1417502F@doc.ic.ac.uk> epa98@doc.ic.ac.uk "Ed Avis" writes:
> Phil Hunt wrote:
> >>Can't you write a template class in C++, and put
> >>it in a dynamically linked library?
> >
> >I would be surprised if this is the case. However instantiations of
> >templates can be put in a DLL or .so.
> 
> What do you mean by 'instantiations of templates'?
> 
> Surely if I write a class like this (pseudocode, I don't know Ada and
> my C++ is rusty):
> 
> class List
>   let T be any class
>   method add(T)
>   method get_first_item : returns T
>   method count_items : returns Int
> 
> then there will only one copy of the executable code in the object
> file.  If the program instantiates a List of Int, then the code for
> List is called and passed pointers (or references) to Ints.  If the
> program wants a List of Char, then the same object code can be used,
> being passed pointers to Chars.
> 
> Or have I got it horribly wrong?

I think you've got it horribly wrong (there might be C++ compilers
that work like that, but I imagine they are very rare, produce slow code
and are horrible to implement).

What C++ does is constructs code for the template with T changed to
int, compiles it, and produces code for the template with T changed
to char, and compiles that as well.

-- 
Phil Hunt....philh@vision25.demon.co.uk