Allow Mojo structs as map keys

mojo/public/cpp/bindings/lib/clone_equals_util.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef MOJO_PUBLIC_CPP_BINDINGS_LIB_CLONE_EQUALS_UTIL_H_
 #define MOJO_PUBLIC_CPP_BINDINGS_LIB_CLONE_EQUALS_UTIL_H_
 
+#include <functional>
 #include <type_traits>
 #include <unordered_map>
 #include <vector>
 
 #include "base/optional.h"
 #include "mojo/public/cpp/bindings/lib/template_util.h"
 
 namespace mojo {
 namespace internal {
 
@@ skipping 130 matching lines @@
     }
     return true;
   }
 };
 
 template <typename T>
 bool Equals(const T& a, const T& b) {
   return EqualsTraits<T>::Equals(a, b);
 }
 
+template <typename T>
+size_t HashCombine(size_t seed, const T& value) {

[yzshen1, 2016/09/20 23:44:39]

Does it make sense to move hash-related functions to a separate file? (and the
same comment for wtf_clone_equals_util.h)

[tibell, 2016/09/21 07:10:53]

Done.

+  // Based on proposal in:
+  // http://www.open-std.org/JTC1/SC22/WG21/docs/papers/2005/n1756.pdf
+  return seed ^ (std::hash<T>()(value) + (seed << 6) + (seed >> 2));
+}
+
+template <typename T>
+struct HasHashMethod {
+  template <typename U>
+  static char Test(decltype(&U::Hash));
+  template <typename U>
+  static int Test(...);
+  static const bool value = sizeof(Test<T>(0)) == sizeof(char);
+
+ private:
+  EnsureTypeIsComplete<T> check_t_;
+};
+
+template <typename T, bool has_hash_method = HasHashMethod<T>::value>
+struct HashTraits;
+
+template <typename T>
+size_t Hash(size_t seed, const T& value);
+
+template <typename T>
+struct HashTraits<T, true> {
+  static size_t Hash(size_t seed, const T& value) { return value.Hash(seed); }
+};
+
+template <typename T>
+struct HashTraits<T, false> {
+  static size_t Hash(size_t seed, const T& value) {
+    return HashCombine(seed, value);
+  }
+};
+
+template <typename T>
+struct HashTraits<base::Optional<T>, false> {

[Sam McNally, 2016/09/21 04:57:58]

If we're still disallowing nullable structs, arrays and maps as map keys, I
don't think we need these specialisations yet. Alternatively, add some tests so
these don't rot.

[tibell, 2016/09/21 07:10:53]

Done. Deleted.

+  static size_t Hash(size_t seed, const base::Optional<T>& value) {
+    return !value ? HashCombine(seed, 0) : internal::Hash(seed, *value);

[yzshen1, 2016/09/20 23:44:39]

nit: is "internal::" necessary here?

[tibell, 2016/09/21 07:10:53]

Done.

+  }
+};
+
+template <typename T>
+struct HashTraits<std::vector<T>, false> {
+  static size_t Hash(size_t seed, const std::vector<T>& value) {
+    for (const auto& element : value) {
+      seed = Hash(seed, element);
+    }
+    return seed;
+  }
+};
+
+template <typename K, typename V>
+struct HashTraits<std::unordered_map<K, V>, false> {
+  static size_t Hash(size_t seed, const std::unordered_map<K, V>& value) {
+    for (const auto& element : value) {
+      seed = Hash(seed, element.first);
+      seed = Hash(seed, element.second);
+    }
+    return seed;
+  }
+};
+
+template <typename T>
+size_t Hash(size_t seed, const T& value) {
+  return HashTraits<T>::Hash(seed, value);
+}
+
 }  // namespace internal
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_LIB_CLONE_EQUALS_UTIL_H_