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Sun, Nov 10, 08:11

aka_static_if.hh
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// Copyright (c) 2016 Vittorio Romeo
// License: AFL 3.0 | https://opensource.org/licenses/AFL-3.0
// http://vittorioromeo.info | vittorio.romeo@outlook.com
#ifndef AKANTU_AKA_STATIC_IF_HH
#define AKANTU_AKA_STATIC_IF_HH
#ifndef AKANTU_ITERATOR_NAMESPACE
#define AKANTU_ITERATOR_NAMESPACE akantu
#endif
#include <utility>
#define FWD(...) ::std::forward<decltype(__VA_ARGS__)>(__VA_ARGS__)
namespace AKANTU_ITERATOR_NAMESPACE {
template <typename TPredicate> auto static_if(TPredicate) noexcept;
namespace impl {
template <bool TPredicateResult> struct static_if_impl;
template <typename TFunctionToCall> struct static_if_result;
template <typename TF> auto make_static_if_result(TF && f) noexcept;
template <> struct static_if_impl<true> {
template <typename TF> auto & else_(TF &&) noexcept {
// Ignore `else_`, as the predicate is true.
return *this;
}
template <typename TPredicate> auto & else_if(TPredicate) noexcept {
// Ignore `else_if`, as the predicate is true.
return *this;
}
template <typename TF> auto then(TF && f) noexcept {
// We found a matching branch, just make a result and
// ignore everything else.
return make_static_if_result(FWD(f));
}
};
template <> struct static_if_impl<false> {
template <typename TF> auto & then(TF &&) noexcept {
// Ignore `then`, as the predicate is false.
return *this;
}
template <typename TF> auto else_(TF && f) noexcept {
// (Assuming that `else_` is after all `else_if` calls.)
// We found a matching branch, just make a result and
// ignore everything else.
return make_static_if_result(FWD(f));
}
template <typename TPredicate> auto else_if(TPredicate) noexcept {
return static_if(TPredicate{});
}
template <typename... Ts> auto operator()(Ts &&...) noexcept {
// If there are no `else` branches, we must ignore calls
// to a failed `static_if` matching.
}
};
template <typename TFunctionToCall>
struct static_if_result : TFunctionToCall {
// Perfect-forward the function in the result instance.
template <typename TFFwd>
explicit static_if_result(TFFwd && f) noexcept : TFunctionToCall(FWD(f)) {}
// Ignore everything, we found a result.
template <typename TF> auto & then(TF &&) noexcept { return *this; }
template <typename TPredicate> auto & else_if(TPredicate) noexcept {
return *this;
}
template <typename TF> auto & else_(TF &&) noexcept { return *this; }
};
template <typename TF> auto make_static_if_result(TF && f) noexcept {
return static_if_result<TF>{FWD(f)};
}
} // namespace impl
template <typename TPredicate> auto static_if(TPredicate) noexcept {
return impl::static_if_impl<TPredicate{}>{};
}
#undef FWD
} // namespace AKANTU_ITERATOR_NAMESPACE
#endif /* AKANTU_AKA_STATIC_IF_HH */

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