folly/Concepts.h

Summary:
We have a need for some common concepts that are used in many places.

This is a proposal, please let me know what you think.

Differential Revision: D59396081

folly/BUCK

@@ -195,6 +195,11 @@ cpp_library(
     ],
 )
 
+cpp_library(
+    name = "concepts",
+    headers = ["Concepts.h"],
+)
+
 cpp_library(
     name = "concurrent_lazy",
     headers = ["ConcurrentLazy.h"],

folly/Concepts.h

@@ -0,0 +1,150 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * 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
+ *
+ *     http://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.
+ */
+
+#pragma once
+
+#include <concepts>
+#include <iterator>
+#include <ranges>
+
+namespace folly {
+
+/*
+ *  Concept to restrict perfect forwarding to a specific type.
+ *
+ *  Example:
+ *    void foo(folly::forwarded<std::vector<int>> auto&& vec);
+ *
+ */
+template <typename Fwd, typename To>
+concept forwarded = std::same_as<std::remove_cvref_t<Fwd>, To>;
+
+/*
+ * T is one of the specified types
+ *
+ * NOTE: doesn't have subsumption with `std::same_as`
+ */
+template <typename T, typename... Ts>
+concept one_of =
+    (std::is_same_v<T, Ts> || // using is_same_v because it's is faster to
+                              // compile and doesn't change behaviour
+     ...);
+
+/*
+ * T implicitly converts to one of the specified types
+ *
+ * NOTE: doesn't have subsumption with `one_of`
+ */
+template <typename From, typename... To>
+concept convertible_to_one_of = (std::is_convertible_v<From, To> || ...);
+
+// iterator_of -----------------------------------------------
+// iterator for range of exacly one of the listed types
+
+template <typename I, typename... Ts>
+concept input_iterator_of =
+    std::input_iterator<I> && one_of<std::iter_value_t<I>, Ts...>;
+
+template <typename I, typename... Ts>
+concept forward_iterator_of =
+    std::forward_iterator<I> && one_of<std::iter_value_t<I>, Ts...>;
+
+template <typename I, typename... Ts>
+concept bidirectional_iterator_of =
+    std::bidirectional_iterator<I> && one_of<std::iter_value_t<I>, Ts...>;
+
+template <typename I, typename... Ts>
+concept random_access_iterator_of =
+    std::random_access_iterator<I> && one_of<std::iter_value_t<I>, Ts...>;
+
+template <typename I, typename... Ts>
+concept contiguous_iterator_of =
+    std::contiguous_iterator<I> && one_of<std::iter_value_t<I>, Ts...>;
+
+// iterator_of_convertible_to -----------------------------------------------
+//  iterator for range of smth convertible to one of the listed types
+
+template <typename I, typename... Ts>
+concept input_iterator_of_convertible_to = std::input_iterator<I> &&
+    convertible_to_one_of<std::iter_value_t<I>, Ts...>;
+
+template <typename I, typename... Ts>
+concept forward_iterator_of_convertible_to = std::forward_iterator<I> &&
+    convertible_to_one_of<std::iter_value_t<I>, Ts...>;
+
+template <typename I, typename... Ts>
+concept bidirectional_iterator_of_convertible_to =
+    std::bidirectional_iterator<I> &&
+    convertible_to_one_of<std::iter_value_t<I>, Ts...>;
+
+template <typename I, typename... Ts>
+concept random_access_iterator_of_convertible_to =
+    std::random_access_iterator<I> &&
+    convertible_to_one_of<std::iter_value_t<I>, Ts...>;
+
+template <typename I, typename... Ts>
+concept contiguous_iterator_of_convertible_to = std::contiguous_iterator<I> &&
+    convertible_to_one_of<std::iter_value_t<I>, Ts...>;
+
+// range_of -----------------------------------------------
+// range of one of the specified types
+
+template <typename R, typename... Ts>
+concept input_range_of =
+    std::ranges::input_range<R> && one_of<std::ranges::range_value_t<R>, Ts...>;
+
+template <typename R, typename... Ts>
+concept forward_range_of = std::ranges::forward_range<R> &&
+    one_of<std::ranges::range_value_t<R>, Ts...>;
+
+template <typename R, typename... Ts>
+concept bidirectional_range_of = std::ranges::bidirectional_range<R> &&
+    one_of<std::ranges::range_value_t<R>, Ts...>;
+
+template <typename R, typename... Ts>
+concept random_access_range_of = std::ranges::random_access_range<R> &&
+    one_of<std::ranges::range_value_t<R>, Ts...>;
+
+template <typename R, typename... Ts>
+concept contiguous_range_of = std::ranges::contiguous_range<R> &&
+    one_of<std::ranges::range_value_t<R>, Ts...>;
+
+// range_of_convertible_to -----------------------------------------------
+// range of one of the specified types
+
+template <typename R, typename... Ts>
+concept input_range_of_convertible_to = std::ranges::input_range<R> &&
+    convertible_to_one_of<std::ranges::range_value_t<R>, Ts...>;
+
+template <typename R, typename... Ts>
+concept forward_range_of_convertible_to = std::ranges::forward_range<R> &&
+    convertible_to_one_of<std::ranges::range_value_t<R>, Ts...>;
+
+template <typename R, typename... Ts>
+concept bidirectional_range_of_convertible_to =
+    std::ranges::bidirectional_range<R> &&
+    convertible_to_one_of<std::ranges::range_value_t<R>, Ts...>;
+
+template <typename R, typename... Ts>
+concept random_access_range_of_convertible_to =
+    std::ranges::random_access_range<R> &&
+    convertible_to_one_of<std::ranges::range_value_t<R>, Ts...>;
+
+template <typename R, typename... Ts>
+concept contiguous_range_of_convertible_to = std::ranges::contiguous_range<R> &&
+    convertible_to_one_of<std::ranges::range_value_t<R>, Ts...>;
+
+} // namespace folly

folly/test/BUCK

@@ -237,6 +237,16 @@ cpp_unittest(
     ],
 )
 
+cpp_unittest(
+    name = "concepts_test",
+    srcs = ["ConceptsTest.cpp"],
+    headers = [],
+    deps = [
+        "//folly:concepts",
+        "//folly/portability:gtest",
+    ],
+)
+
 cpp_benchmark(
     name = "concurrent_skip_list_benchmark",
     srcs = ["ConcurrentSkipListBenchmark.cpp"],