Add public aliases for default hash/eq types in hash-based containers

Generic user code sometimes wants to provide more flexibility for its
own users and provide type arguments that are used as Hash/Eq in
underlying containers.

However, there is no sensible publicly available default value for it
yet.

This CL fixes this issue and provides publicly visible aliases that such
user code can use.

PiperOrigin-RevId: 627844757
Change-Id: I4c393007244ad8d998da02883c623eae1715c0df

1 files changed, 45 insertions, 0 deletions

diff --git a/absl/container/hash_container_defaults.h b/absl/container/hash_container_defaults.h
new file mode 100644
index 00000000..eb944a7c
--- /dev/null
+++ b/absl/container/hash_container_defaults.h
@@ -0,0 +1,45 @@
+// Copyright 2024 The Abseil Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef ABSL_CONTAINER_HASH_CONTAINER_DEFAULTS_H_
+#define ABSL_CONTAINER_HASH_CONTAINER_DEFAULTS_H_
+
+#include "absl/base/config.h"
+#include "absl/container/internal/hash_function_defaults.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+// DefaultHashContainerHash is a convenience alias for the functor that is used
+// by default by Abseil hash-based (unordered) containers for hashing when
+// `Hash` type argument is not explicitly specified.
+//
+// This type alias can be used by generic code that wants to provide more
+// flexibility for defining underlying containers.
+template <typename T>
+using DefaultHashContainerHash = absl::container_internal::hash_default_hash<T>;
+
+// DefaultHashContainerEq is a convenience alias for the functor that is used by
+// default by Abseil hash-based (unordered) containers for equality check when
+// `Eq` type argument is not explicitly specified.
+//
+// This type alias can be used by generic code that wants to provide more
+// flexibility for defining underlying containers.
+template <typename T>
+using DefaultHashContainerEq = absl::container_internal::hash_default_eq<T>;
+
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_CONTAINER_HASH_CONTAINER_DEFAULTS_H_