Re: GPL and "free" software

["Nick Roberts" <nickroberts@callnetuk.com>]

Very briefly, C++ templates and Ada generics provide a way to encode an
algorithm only once, if it is the kind of algorithm which can be applied
unchanged to several variations of things that are basically 'static' in
languages such as C++ and Ada (types, functions/subprograms, etc.).  Each
such variation is called an 'instance', and setting up an instance ready for
use is called 'instantiation'.  C++ templates and Ada generic units work in
fundamentally the same way; the biggest difference being that, in C++,
templates are instantiated automatically.

The usual (default) implementation is for each instantiation of a template
or generic unit to cause the creation of a new piece of object code, varied
according to the template/generic parameters.  (This generally gives faster
execution speed, but at the cost of the overall program's object code being
bigger.)

But, some implementations (optionally) produce a single piece of object
code, which calls 'hooks' inside it to provide the variation according to
the different template/generic parameters; each instantiation then simply
generates a set of appropriate hooks.  A pointer to one of these sets of
hooks must be passed in on every call into the template/generic.  (This
generally gives slower speed, but reduces the size of the overall program's
object code.)

There are other schemes which provide a compromise between these two
extremes.

I think the relevant point is that, in any eventuality, if a program uses a
template or generic unit, then some object code corresponding to that
template or generic unit will end up in the program's object code.  I feel
sure it is the case that the source code for many templates and generic
units will constitute an 'original and substantive work' susceptible to a
claim of copyright.

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Nick Roberts
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