Greg Colvin wrote:
> > If it was run-time C++, I would be happy with 'apply_tuple',
> > but in MPL domain "tuple" isn't really the right word, and I
> > don't like 'apply_seq' or, worse yet, 'apply_sequence'. Or
> > should it be 'seq_apply' (from an English language standpoint)?
>
> If this construct applies a metafuntion to a sequence
It does and it doesn't :). Sorry if I wasn't clear about the semantics; it
does not apply a metafunction to every element of a sequence;
instead, it unrolls the sequence and passes all its elements to the
metafunction as separate arguments, all at once.
To clarify it further, here's how a run-time equivalent of that hypothetical
'apply_tuple' could look like:
template< typename F, typename Tuple >
typename result_type<F>::type
do_apply(F f, Tuple const& args, arity<1>)
{
return f(get<0>(args));
}
template< typename F, typename Tuple >
typename result_type<F>::type
do_apply(F f, Tuple const& args, arity<2>)
{
return f(get<0>(args), get<1>(args));
}
// ...
template< typename F, typename Tuple >
typename result_type<F>::type
apply(F f, Tuple const& args)
{
enum { n = tuple_length<Tuple>::value };
return do_apply(f, args, arity<n>());
}
void f(int, char const*);
int main()
{
apply(f, make_tuple(5, "text")); // here
}
> then "apply_to_sequence" would be an accurate name.
Thanks for clarifying the language side. Would it be still accurate for the
aforementioned semantics?
> Too bad it can't just be "apply".
Yeah, unfortunately it can't be. You have to have different notation for
invoking a function with a sequence of elements, 'cause just determining if
the first and the only argument is a sequence and unrolling it is not enough
- a (meta)function itself might expect exactly the original sequence, after
all.
Thanks,
Aleksey
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