Re: [linux-audio-dev] C++ wrapper for libsndfile

On Sat, 2006-07-29 at 23:14 +1000, Erik de Castro Lopo wrote:
> Lars Luthman wrote:
>
> > The 4 different overloaded versions of the read, readf, write, and
> > writef functions will cause ambiguities that will force you to cast them
> > to their respective types in order to use pointers to them, for example
> > in functors (e.g. a sigc++ slot), like this:
> >
> > mem_fun(sndobj, (sf_count_t (Sndfile::*)(float*,
> > sf_count_t))&Sndfile::read);
> >
> > If they were specialisations of the same template functions instead,
> > with the sample type as template parameter, you'd only have to write
> > this:
> >
> > mem_fun(sndobj, &Sndfile::read<float>);
> >
> > which is a lot nicer and easier to read.
>
> Interesting use case.
>
> I'm not even close to being an expert in C++ templates, but
> I suppose that read function would then be defined as something
> like:
>
> template <T> sf_count_t read (T *ptr, sf_count_t items) ;
>
> SO how do I ensure that <T> only gets specialised as short,
> int, float and double?

class Sndfile {
 ...
 template <typename T> sf_count_t read (T *ptr, sf_count_t items);
 ...
};

template <> sf_count_t Sndfile::read<short>(short* ptr, sf_count_t
items) { ... }
template <> sf_count_t Sndfile::read<int>(int* ptr, sf_count_t items)
{ ... }
template <> sf_count_t Sndfile::read<float>(float* ptr, sf_count_t
items) { ... }
template <> sf_count_t Sndfile::read<double>(double* ptr, sf_count_t
items) { ... }

...and nothing more. If you don't have a generic implementation anyone
who tries to instantiate the template with an unsupported type will get
a compilation error.

I don't think there is a way to actually prevent someone else from
writing a generic implementation or a different specialisation in their
own source, but if they try that they should _really_ know what they are
doing.

-- 
Lars Luthman - please encrypt any email sent to me if possible
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