Allow Mojo structs as map keys

mojo/public/cpp/bindings/lib/wtf_hash_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_WTF_HASH_UTIL_H_
+#define MOJO_PUBLIC_CPP_BINDINGS_LIB_WTF_HASH_UTIL_H_
+
+#include <type_traits>
+
+#include "mojo/public/cpp/bindings/lib/hash_util.h"
+#include "mojo/public/cpp/bindings/struct_ptr.h"
+#include "third_party/WebKit/Source/wtf/HashFunctions.h"
+#include "third_party/WebKit/Source/wtf/text/StringHash.h"
+#include "third_party/WebKit/Source/wtf/text/WTFString.h"
+
+namespace mojo {
+namespace internal {
+
+template <typename T>
+size_t WTFHashCombine(size_t seed, const T& value) {
+  // Based on proposal in:
+  // http://www.open-std.org/JTC1/SC22/WG21/docs/papers/2005/n1756.pdf
+  //
+  // TODO(tibell): We'd like to use WTF::DefaultHash here instead, but currently
+  //     there are no general instance for enums and their can't be an instance

[yzshen1, 2016/09/22 23:48:56]

I cannot parse this sentence. (Is it because "their" should be "there"?)

[tibell, 2016/09/23 00:07:07]

Better now?

+  //     for bool for that trait.
+  return seed ^ (std::hash<T>()(value) + (seed << 6) + (seed >> 2));
+}
+
+template <typename T, bool has_hash_method = HasHashMethod<T>::value>
+struct WTFHashTraits;

[tibell, 2016/09/22 07:30:25]

This trait exists separately from HashTraits so that we

 * can eventually fix the TODO above (by calling DefaultHash<T>::Hash::hash
instead of std::hash there) and
 * have a natural place to put an instance for WTF::String.

I didn't have both HashTraits and WTFHashTraits initially. Worth keeping?

+
+template <typename T>
+size_t WTFHash(size_t seed, const T& value);
+
+template <typename T>
+struct WTFHashTraits<T, true> {
+  static size_t Hash(size_t seed, const T& value) { return value.Hash(seed); }
+};
+
+template <typename T>
+struct WTFHashTraits<T, false> {
+  static size_t Hash(size_t seed, const T& value) {
+    return WTFHashCombine(seed, value);
+  }
+};
+
+template <>
+struct WTFHashTraits<WTF::String, false> {
+  static size_t Hash(size_t seed, const WTF::String& value) {
+    return HashCombine(seed, WTF::StringHash::hash(value));
+  }
+};
+
+template <typename T>
+size_t WTFHash(size_t seed, const T& value) {
+  return WTFHashTraits<T>::Hash(seed, value);
+}
+
+template <typename T>
+struct StructPtrHashFn {
+  static unsigned hash(const StructPtr<T>& value) {
+    return value.Hash(kHashSeed);
+  }
+  static bool equal(const StructPtr<T>& left, const StructPtr<T>& right) {
+    return left.Equals(right);
+  }
+  static const bool safeToCompareToEmptyOrDeleted = false;
+};
+
+template <typename T>
+struct InlinedStructPtrHashFn {
+  static unsigned hash(const InlinedStructPtr<T>& value) {
+    return value.Hash(kHashSeed);
+  }
+  static bool equal(const InlinedStructPtr<T>& left,
+                    const InlinedStructPtr<T>& right) {
+    return left.Equals(right);
+  }
+  static const bool safeToCompareToEmptyOrDeleted = false;
+};
+
+}  // namespace internal
+}  // namespace mojo
+
+namespace WTF {
+
+template <typename T>
+struct DefaultHash<mojo::StructPtr<T>> {
+  using Hash = mojo::internal::StructPtrHashFn<T>;
+};
+
+template <typename T>
+struct HashTraits<mojo::StructPtr<T>>
+    : public GenericHashTraits<mojo::StructPtr<T>> {
+  static const bool hasIsEmptyValueFunction = true;
+  static bool isEmptyValue(const mojo::StructPtr<T>& value) {
+    return value.is_null();
+  }
+  static void constructDeletedValue(mojo::StructPtr<T>& slot, bool) {
+    mojo::internal::StructPtrWTFHelper<T>::ConstructDeletedValue(slot);
+  }
+  static bool isDeletedValue(const mojo::StructPtr<T>& value) {
+    return mojo::internal::StructPtrWTFHelper<T>::IsHashTableDeletedValue(
+        value);
+  }
+};
+
+template <typename T>
+struct DefaultHash<mojo::InlinedStructPtr<T>> {
+  using Hash = mojo::internal::InlinedStructPtrHashFn<T>;
+};
+
+template <typename T>
+struct HashTraits<mojo::InlinedStructPtr<T>>
+    : public GenericHashTraits<mojo::InlinedStructPtr<T>> {
+  static const bool hasIsEmptyValueFunction = true;
+  static bool isEmptyValue(const mojo::InlinedStructPtr<T>& value) {
+    return value.is_null();
+  }
+  static void constructDeletedValue(mojo::InlinedStructPtr<T>& slot, bool) {
+    mojo::internal::InlinedStructPtrWTFHelper<T>::ConstructDeletedValue(slot);
+  }
+  static bool isDeletedValue(const mojo::InlinedStructPtr<T>& value) {
+    return mojo::internal::InlinedStructPtrWTFHelper<
+        T>::IsHashTableDeletedValue(value);
+  }
+};
+
+}  // namespace WTF
+
+#endif  // MOJO_PUBLIC_CPP_BINDINGS_LIB_WTF_HASH_UTIL_H_