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BeefySysLib/third_party/sparsehash/sparsehash/template_util.h

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+// Copyright 2005 Google Inc.
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// ----
+//
+// Template metaprogramming utility functions.
+//
+// This code is compiled directly on many platforms, including client
+// platforms like Windows, Mac, and embedded systems.  Before making
+// any changes here, make sure that you're not breaking any platforms.
+//
+//
+// The names choosen here reflect those used in tr1 and the boost::mpl
+// library, there are similar operations used in the Loki library as
+// well.  I prefer the boost names for 2 reasons:
+// 1.  I think that portions of the Boost libraries are more likely to
+// be included in the c++ standard.
+// 2.  It is not impossible that some of the boost libraries will be
+// included in our own build in the future.
+// Both of these outcomes means that we may be able to directly replace
+// some of these with boost equivalents.
+//
+#ifndef BASE_TEMPLATE_UTIL_H_
+#define BASE_TEMPLATE_UTIL_H_
+
+#include <sparsehash/internal/sparseconfig.h>
+_START_GOOGLE_NAMESPACE_
+
+// Types small_ and big_ are guaranteed such that sizeof(small_) <
+// sizeof(big_)
+typedef char small_;
+
+struct big_ {
+  char dummy[2];
+};
+
+// Identity metafunction.
+template <class T>
+struct identity_ {
+  typedef T type;
+};
+
+// integral_constant, defined in tr1, is a wrapper for an integer
+// value. We don't really need this generality; we could get away
+// with hardcoding the integer type to bool. We use the fully
+// general integer_constant for compatibility with tr1.
+
+template<class T, T v>
+struct integral_constant {
+  static const T value = v;
+  typedef T value_type;
+  typedef integral_constant<T, v> type;
+};
+
+template <class T, T v> const T integral_constant<T, v>::value;
+
+
+// Abbreviations: true_type and false_type are structs that represent boolean
+// true and false values. Also define the boost::mpl versions of those names,
+// true_ and false_.
+typedef integral_constant<bool, true>  true_type;
+typedef integral_constant<bool, false> false_type;
+typedef true_type  true_;
+typedef false_type false_;
+
+// if_ is a templatized conditional statement.
+// if_<cond, A, B> is a compile time evaluation of cond.
+// if_<>::type contains A if cond is true, B otherwise.
+template<bool cond, typename A, typename B>
+struct if_{
+  typedef A type;
+};
+
+template<typename A, typename B>
+struct if_<false, A, B> {
+  typedef B type;
+};
+
+
+// type_equals_ is a template type comparator, similar to Loki IsSameType.
+// type_equals_<A, B>::value is true iff "A" is the same type as "B".
+//
+// New code should prefer base::is_same, defined in base/type_traits.h.
+// It is functionally identical, but is_same is the standard spelling.
+template<typename A, typename B>
+struct type_equals_ : public false_ {
+};
+
+template<typename A>
+struct type_equals_<A, A> : public true_ {
+};
+
+// and_ is a template && operator.
+// and_<A, B>::value evaluates "A::value && B::value".
+template<typename A, typename B>
+struct and_ : public integral_constant<bool, (A::value && B::value)> {
+};
+
+// or_ is a template || operator.
+// or_<A, B>::value evaluates "A::value || B::value".
+template<typename A, typename B>
+struct or_ : public integral_constant<bool, (A::value || B::value)> {
+};
+
+
+_END_GOOGLE_NAMESPACE_
+
+#endif  // BASE_TEMPLATE_UTIL_H_