currying.qbk
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[#currying]
[section Currying]
A [link metafunction template metafunction] supports ['currying] when it accepts
less arguments than it normally expects. When less arguments are provided, then
it returns a [link metafunction_class template metafunction class] expecting
the remaining arguments. That template metafunction class is also expected to
support currying.
For example assuming the following metafunction is given:
template <class A, class B>
struct plus;
It takes two values, adds them and returns their result. For example:
static_assert(
plus<
std::integral_constant<int, 11>,
std::integral_constant<int, 2>
>::type::value == 13,
"This should work"
);
If it supports currying, then the following should also work:
using inc = plus<std::integral_constant<int, 1>>;
static_assert(
inc::apply<std::integral_constant<int, 12>>::type::value == 13,
"This should work"
);
The above example defines the `inc` template metafunction class by calling
`plus` with just one argument: the [link boxed_value boxed] `1` value.
[endsect]