71 lines
2.1 KiB
C++
71 lines
2.1 KiB
C++
/*
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* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/.
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*
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* Copyright 2017-2019 Danny Robson <danny@nerdcruft.net>
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*/
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#pragma once
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#include <atomic>
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#include <variant>
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namespace cruft {
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namespace detail {
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template <typename TagT>
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int typeidx_next (void)
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{
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static std::atomic<int> counter;
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return ++counter;
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}
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}
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/// Return a globally unique runtime ID for a given type (namespaced by a
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/// tag type).
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///
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/// This is intended to be used as a lightweight type check for variants
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/// and such without requiring RTTI.
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///
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/// The identifier is constructed at runtime and is not guaranteed to be
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/// stable across executions (particularly in the case of threads and
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/// other non-determinism). However it _is_ threadsafe to call this.
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///
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/// The value 0 will never be returned from this function and can be used
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/// to indicate an 'unknown' state.
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///
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/// The range of identifiers is _probably_ contiguous. This should not
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/// be relied upon for correctness, but may be used for performance
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/// concerns.
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///
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/// \tparam T The type to register-and-retrieve the ID for
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/// \tparam TagT A namespacing type; different tags will have different
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/// sets of IDs. The default Tag is void.
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/// \return The unique ID of the type
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template <typename T, typename TagT = void>
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int
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typeidx (void)
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{
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static auto id = detail::typeidx_next<TagT> ();
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return id;
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}
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/// Returns the typeidx of the contained value within a variant.
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///
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/// May throw std::bad_variant_access if the variant is
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/// valueless_by_exception.
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template <typename TagT=void, typename ...ComponentT>
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int
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value_typeidx (std::variant<ComponentT...> const &val)
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{
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return std::visit (
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[] <typename ValueT> (ValueT const &) {
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return typeidx<ValueT> ();
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},
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val
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);
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}
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}
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