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-rw-r--r--absl/functional/BUILD.bazel26
-rw-r--r--absl/functional/bind_front.h152
-rw-r--r--absl/functional/bind_front_test.cc231
-rw-r--r--absl/functional/internal/front_binder.h95
4 files changed, 504 insertions, 0 deletions
diff --git a/absl/functional/BUILD.bazel b/absl/functional/BUILD.bazel
index 0a7b588e..432546ce 100644
--- a/absl/functional/BUILD.bazel
+++ b/absl/functional/BUILD.bazel
@@ -27,6 +27,32 @@ package(default_visibility = ["//visibility:public"])
licenses(["notice"]) # Apache 2.0
cc_library(
+ name = "bind_front",
+ srcs = ["internal/front_binder.h"],
+ hdrs = ["bind_front.h"],
+ copts = ABSL_DEFAULT_COPTS,
+ linkopts = ABSL_DEFAULT_LINKOPTS,
+ deps = [
+ "//absl/base:base_internal",
+ "//absl/container:compressed_tuple",
+ "//absl/meta:type_traits",
+ "//absl/utility",
+ ],
+)
+
+cc_test(
+ name = "bind_front_test",
+ srcs = ["bind_front_test.cc"],
+ copts = ABSL_TEST_COPTS,
+ linkopts = ABSL_DEFAULT_LINKOPTS,
+ deps = [
+ ":bind_front",
+ "//absl/memory",
+ "@com_google_googletest//:gtest_main",
+ ],
+)
+
+cc_library(
name = "function_ref",
srcs = ["internal/function_ref.h"],
hdrs = ["function_ref.h"],
diff --git a/absl/functional/bind_front.h b/absl/functional/bind_front.h
new file mode 100644
index 00000000..4c61d0ec
--- /dev/null
+++ b/absl/functional/bind_front.h
@@ -0,0 +1,152 @@
+// Copyright 2018 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.
+
+// `absl::bind_front()` returns a functor by binding a number of arguments to
+// the front of a provided functor, allowing you to avoid known problems with
+// `std::bind()`. It is a form of partial function application
+// https://en.wikipedia.org/wiki/Partial_application.
+//
+// Like `std::bind()` it is implicitly convertible to `std::function`. In
+// particular, it may be used as a simpler replacement for `std::bind()` in most
+// cases, as it does not require placeholders to be specified. More
+// importantly, it provides more reliable correctness guarantees than
+// `std::bind()`.
+//
+// absl::bind_front(a...) can be seen as storing the results of
+// std::make_tuple(a...).
+//
+// Example: Binding a free function.
+//
+// int Minus(int a, int b) { return a - b; }
+//
+// assert(absl::bind_front(Minus)(3, 2) == 3 - 2);
+// assert(absl::bind_front(Minus, 3)(2) == 3 - 2);
+// assert(absl::bind_front(Minus, 3, 2)() == 3 - 2);
+//
+// Example: Binding a member function.
+//
+// struct Math {
+// int Double(int a) const { return 2 * a; }
+// };
+//
+// Math math;
+//
+// assert(absl::bind_front(&Math::Double)(&math, 3) == 2 * 3);
+// // Stores a pointer to math inside the functor.
+// assert(absl::bind_front(&Math::Double, &math)(3) == 2 * 3);
+// // Stores a copy of math inside the functor.
+// assert(absl::bind_front(&Math::Double, math)(3) == 2 * 3);
+// // Stores std::unique_ptr<Math> inside the functor.
+// assert(absl::bind_front(&Math::Double,
+// std::unique_ptr<Math>(new Math))(3) == 2 * 3);
+//
+// Example: Using `absl::bind_front()`, instead of `std::bind()`, with
+// `std::function`.
+//
+// class FileReader {
+// public:
+// void ReadFileAsync(const std::string& filename, std::string* content,
+// const std::function<void()>& done) {
+// // Calls Executor::Schedule(std::function<void()>).
+// Executor::DefaultExecutor()->Schedule(
+// absl::bind_front(&FileReader::BlockingRead, this,
+// filename, content, done));
+// }
+//
+// private:
+// void BlockingRead(const std::string& filename, std::string* content,
+// const std::function<void()>& done) {
+// CHECK_OK(file::GetContents(filename, content, {}));
+// done();
+// }
+// };
+//
+// `absl::bind_front()` stores bound arguments explicitly using the type passed
+// rather than implicitly based on the type accepted by its functor.
+//
+// Example: Binding arguments explicitly.
+//
+// void LogStringView(absl::string_view sv) {
+// LOG(INFO) << sv;
+// }
+//
+// Executor* e = Executor::DefaultExecutor();
+// std::string s = "hello";
+// absl::string_view sv = s;
+//
+// // absl::bind_front(LogStringView, arg) makes a copy of arg and stores it.
+// e->Schedule(absl::bind_front(LogStringView, sv)); // ERROR: dangling
+// // string_view.
+//
+// e->Schedule(absl::bind_front(LogStringView, s)); // OK: stores a copy of
+// // s.
+//
+// To store some of the arguments passed to `absl::bind_front()` by reference,
+// use std::ref()` and `std::cref()`.
+//
+// Example: Storing some of the bound arguments by reference.
+//
+// class Service {
+// public:
+// void Serve(const Request& req, std::function<void()>* done) {
+// // The request protocol buffer won't be deleted until done is called.
+// // It's safe to store a reference to it inside the functor.
+// Executor::DefaultExecutor()->Schedule(
+// absl::bind_front(&Service::BlockingServe, this, std::cref(req),
+// done));
+// }
+//
+// private:
+// void BlockingServe(const Request& req, std::function<void()>* done);
+// };
+//
+// Example: Storing bound arguments by reference.
+//
+// void Print(const string& a, const string& b) { LOG(INFO) << a << b; }
+//
+// std::string hi = "Hello, ";
+// std::vector<std::string> names = {"Chuk", "Gek"};
+// // Doesn't copy hi.
+// for_each(names.begin(), names.end(),
+// absl::bind_front(Print, std::ref(hi)));
+//
+// // DO NOT DO THIS: the functor may outlive "hi", resulting in
+// // dangling references.
+// foo->DoInFuture(absl::bind_front(Print, std::ref(hi), "Guest")); // BAD!
+// auto f = absl::bind_front(Print, std::ref(hi), "Guest"); // BAD!
+
+#ifndef ABSL_FUNCTIONAL_BIND_FRONT_H_
+#define ABSL_FUNCTIONAL_BIND_FRONT_H_
+
+#include "absl/functional/internal/front_binder.h"
+#include "absl/utility/utility.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+// Binds the first N arguments of an invocable object and stores them by value,
+// except types of std::reference_wrapper which are 'unwound' and stored by
+// reference.
+template <class F, class... BoundArgs>
+constexpr functional_internal::bind_front_t<F, BoundArgs...> bind_front(
+ F&& func, BoundArgs&&... args) {
+ return functional_internal::bind_front_t<F, BoundArgs...>(
+ absl::in_place, absl::forward<F>(func),
+ absl::forward<BoundArgs>(args)...);
+}
+
+ABSL_NAMESPACE_END
+} // namespace absl
+
+#endif // ABSL_FUNCTIONAL_BIND_FRONT_H_
diff --git a/absl/functional/bind_front_test.cc b/absl/functional/bind_front_test.cc
new file mode 100644
index 00000000..4801a81c
--- /dev/null
+++ b/absl/functional/bind_front_test.cc
@@ -0,0 +1,231 @@
+// Copyright 2018 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.
+
+#include "absl/functional/bind_front.h"
+
+#include <stddef.h>
+
+#include <functional>
+#include <memory>
+#include <string>
+
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+#include "absl/memory/memory.h"
+
+namespace {
+
+char CharAt(const char* s, size_t index) { return s[index]; }
+
+TEST(BindTest, Basics) {
+ EXPECT_EQ('C', absl::bind_front(CharAt)("ABC", 2));
+ EXPECT_EQ('C', absl::bind_front(CharAt, "ABC")(2));
+ EXPECT_EQ('C', absl::bind_front(CharAt, "ABC", 2)());
+}
+
+TEST(BindTest, Lambda) {
+ auto lambda = [](int x, int y, int z) { return x + y + z; };
+ EXPECT_EQ(6, absl::bind_front(lambda)(1, 2, 3));
+ EXPECT_EQ(6, absl::bind_front(lambda, 1)(2, 3));
+ EXPECT_EQ(6, absl::bind_front(lambda, 1, 2)(3));
+ EXPECT_EQ(6, absl::bind_front(lambda, 1, 2, 3)());
+}
+
+struct Functor {
+ std::string operator()() & { return "&"; }
+ std::string operator()() const& { return "const&"; }
+ std::string operator()() && { return "&&"; }
+ std::string operator()() const&& { return "const&&"; }
+};
+
+TEST(BindTest, PerfectForwardingOfBoundArgs) {
+ auto f = absl::bind_front(Functor());
+ const auto& cf = f;
+ EXPECT_EQ("&", f());
+ EXPECT_EQ("const&", cf());
+ EXPECT_EQ("&&", std::move(f)());
+ EXPECT_EQ("const&&", std::move(cf)());
+}
+
+struct ArgDescribe {
+ std::string operator()(int&) const { return "&"; } // NOLINT
+ std::string operator()(const int&) const { return "const&"; } // NOLINT
+ std::string operator()(int&&) const { return "&&"; }
+ std::string operator()(const int&&) const { return "const&&"; }
+};
+
+TEST(BindTest, PerfectForwardingOfFreeArgs) {
+ ArgDescribe f;
+ int i;
+ EXPECT_EQ("&", absl::bind_front(f)(static_cast<int&>(i)));
+ EXPECT_EQ("const&", absl::bind_front(f)(static_cast<const int&>(i)));
+ EXPECT_EQ("&&", absl::bind_front(f)(static_cast<int&&>(i)));
+ EXPECT_EQ("const&&", absl::bind_front(f)(static_cast<const int&&>(i)));
+}
+
+struct NonCopyableFunctor {
+ NonCopyableFunctor() = default;
+ NonCopyableFunctor(const NonCopyableFunctor&) = delete;
+ NonCopyableFunctor& operator=(const NonCopyableFunctor&) = delete;
+ const NonCopyableFunctor* operator()() const { return this; }
+};
+
+TEST(BindTest, RefToFunctor) {
+ // It won't copy/move the functor and use the original object.
+ NonCopyableFunctor ncf;
+ auto bound_ncf = absl::bind_front(std::ref(ncf));
+ auto bound_ncf_copy = bound_ncf;
+ EXPECT_EQ(&ncf, bound_ncf_copy());
+}
+
+struct Struct {
+ std::string value;
+};
+
+TEST(BindTest, StoreByCopy) {
+ Struct s = {"hello"};
+ auto f = absl::bind_front(&Struct::value, s);
+ auto g = f;
+ EXPECT_EQ("hello", f());
+ EXPECT_EQ("hello", g());
+ EXPECT_NE(&s.value, &f());
+ EXPECT_NE(&s.value, &g());
+ EXPECT_NE(&g(), &f());
+}
+
+struct NonCopyable {
+ explicit NonCopyable(const std::string& s) : value(s) {}
+ NonCopyable(const NonCopyable&) = delete;
+ NonCopyable& operator=(const NonCopyable&) = delete;
+
+ std::string value;
+};
+
+const std::string& GetNonCopyableValue(const NonCopyable& n) { return n.value; }
+
+TEST(BindTest, StoreByRef) {
+ NonCopyable s("hello");
+ auto f = absl::bind_front(&GetNonCopyableValue, std::ref(s));
+ EXPECT_EQ("hello", f());
+ EXPECT_EQ(&s.value, &f());
+ auto g = std::move(f); // NOLINT
+ EXPECT_EQ("hello", g());
+ EXPECT_EQ(&s.value, &g());
+ s.value = "goodbye";
+ EXPECT_EQ("goodbye", g());
+}
+
+TEST(BindTest, StoreByCRef) {
+ NonCopyable s("hello");
+ auto f = absl::bind_front(&GetNonCopyableValue, std::cref(s));
+ EXPECT_EQ("hello", f());
+ EXPECT_EQ(&s.value, &f());
+ auto g = std::move(f); // NOLINT
+ EXPECT_EQ("hello", g());
+ EXPECT_EQ(&s.value, &g());
+ s.value = "goodbye";
+ EXPECT_EQ("goodbye", g());
+}
+
+const std::string& GetNonCopyableValueByWrapper(
+ std::reference_wrapper<NonCopyable> n) {
+ return n.get().value;
+}
+
+TEST(BindTest, StoreByRefInvokeByWrapper) {
+ NonCopyable s("hello");
+ auto f = absl::bind_front(GetNonCopyableValueByWrapper, std::ref(s));
+ EXPECT_EQ("hello", f());
+ EXPECT_EQ(&s.value, &f());
+ auto g = std::move(f);
+ EXPECT_EQ("hello", g());
+ EXPECT_EQ(&s.value, &g());
+ s.value = "goodbye";
+ EXPECT_EQ("goodbye", g());
+}
+
+TEST(BindTest, StoreByPointer) {
+ NonCopyable s("hello");
+ auto f = absl::bind_front(&NonCopyable::value, &s);
+ EXPECT_EQ("hello", f());
+ EXPECT_EQ(&s.value, &f());
+ auto g = std::move(f);
+ EXPECT_EQ("hello", g());
+ EXPECT_EQ(&s.value, &g());
+}
+
+int Sink(std::unique_ptr<int> p) {
+ return *p;
+}
+
+std::unique_ptr<int> Factory(int n) { return absl::make_unique<int>(n); }
+
+TEST(BindTest, NonCopyableArg) {
+ EXPECT_EQ(42, absl::bind_front(Sink)(absl::make_unique<int>(42)));
+ EXPECT_EQ(42, absl::bind_front(Sink, absl::make_unique<int>(42))());
+}
+
+TEST(BindTest, NonCopyableResult) {
+ EXPECT_THAT(absl::bind_front(Factory)(42), ::testing::Pointee(42));
+ EXPECT_THAT(absl::bind_front(Factory, 42)(), ::testing::Pointee(42));
+}
+
+// is_copy_constructible<FalseCopyable<unique_ptr<T>> is true but an attempt to
+// instantiate the copy constructor leads to a compile error. This is similar
+// to how standard containers behave.
+template <class T>
+struct FalseCopyable {
+ FalseCopyable() {}
+ FalseCopyable(const FalseCopyable& other) : m(other.m) {}
+ FalseCopyable(FalseCopyable&& other) : m(std::move(other.m)) {}
+ T m;
+};
+
+int GetMember(FalseCopyable<std::unique_ptr<int>> x) { return *x.m; }
+
+TEST(BindTest, WrappedMoveOnly) {
+ FalseCopyable<std::unique_ptr<int>> x;
+ x.m = absl::make_unique<int>(42);
+ auto f = absl::bind_front(&GetMember, std::move(x));
+ EXPECT_EQ(42, std::move(f)());
+}
+
+int Plus(int a, int b) { return a + b; }
+
+TEST(BindTest, ConstExpr) {
+ constexpr auto f = absl::bind_front(CharAt);
+ EXPECT_EQ(f("ABC", 1), 'B');
+ static constexpr int five = 5;
+ constexpr auto plus5 = absl::bind_front(Plus, five);
+ EXPECT_EQ(plus5(1), 6);
+
+ // There seems to be a bug in MSVC dealing constexpr construction of
+ // char[]. Notice 'plus5' above; 'int' works just fine.
+#if !(defined(_MSC_VER) && _MSC_VER < 1910)
+ static constexpr char data[] = "DEF";
+ constexpr auto g = absl::bind_front(CharAt, data);
+ EXPECT_EQ(g(1), 'E');
+#endif
+}
+
+struct ManglingCall {
+ int operator()(int, double, std::string) const { return 0; }
+};
+
+TEST(BindTest, Mangling) {
+ // We just want to generate a particular instantiation to see its mangling.
+ absl::bind_front(ManglingCall{}, 1, 3.3)("A");
+}
+
+} // namespace
diff --git a/absl/functional/internal/front_binder.h b/absl/functional/internal/front_binder.h
new file mode 100644
index 00000000..a4d95da4
--- /dev/null
+++ b/absl/functional/internal/front_binder.h
@@ -0,0 +1,95 @@
+// Copyright 2018 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.
+
+// Implementation details for `absl::bind_front()`.
+
+#ifndef ABSL_FUNCTIONAL_INTERNAL_FRONT_BINDER_H_
+#define ABSL_FUNCTIONAL_INTERNAL_FRONT_BINDER_H_
+
+#include <cstddef>
+#include <type_traits>
+#include <utility>
+
+#include "absl/base/internal/invoke.h"
+#include "absl/container/internal/compressed_tuple.h"
+#include "absl/meta/type_traits.h"
+#include "absl/utility/utility.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace functional_internal {
+
+// Invoke the method, expanding the tuple of bound arguments.
+template <class R, class Tuple, size_t... Idx, class... Args>
+R Apply(Tuple&& bound, absl::index_sequence<Idx...>, Args&&... free) {
+ return base_internal::Invoke(
+ absl::forward<Tuple>(bound).template get<Idx>()...,
+ absl::forward<Args>(free)...);
+}
+
+template <class F, class... BoundArgs>
+class FrontBinder {
+ using BoundArgsT = absl::container_internal::CompressedTuple<F, BoundArgs...>;
+ using Idx = absl::make_index_sequence<sizeof...(BoundArgs) + 1>;
+
+ BoundArgsT bound_args_;
+
+ public:
+ template <class... Ts>
+ constexpr explicit FrontBinder(absl::in_place_t, Ts&&... ts)
+ : bound_args_(absl::forward<Ts>(ts)...) {}
+
+ template <class... FreeArgs,
+ class R = base_internal::InvokeT<F&, BoundArgs&..., FreeArgs&&...>>
+ R operator()(FreeArgs&&... free_args) & {
+ return functional_internal::Apply<R>(bound_args_, Idx(),
+ absl::forward<FreeArgs>(free_args)...);
+ }
+
+ template <class... FreeArgs,
+ class R = base_internal::InvokeT<const F&, const BoundArgs&...,
+ FreeArgs&&...>>
+ R operator()(FreeArgs&&... free_args) const& {
+ return functional_internal::Apply<R>(bound_args_, Idx(),
+ absl::forward<FreeArgs>(free_args)...);
+ }
+
+ template <class... FreeArgs, class R = base_internal::InvokeT<
+ F&&, BoundArgs&&..., FreeArgs&&...>>
+ R operator()(FreeArgs&&... free_args) && {
+ // This overload is called when *this is an rvalue. If some of the bound
+ // arguments are stored by value or rvalue reference, we move them.
+ return functional_internal::Apply<R>(absl::move(bound_args_), Idx(),
+ absl::forward<FreeArgs>(free_args)...);
+ }
+
+ template <class... FreeArgs,
+ class R = base_internal::InvokeT<const F&&, const BoundArgs&&...,
+ FreeArgs&&...>>
+ R operator()(FreeArgs&&... free_args) const&& {
+ // This overload is called when *this is an rvalue. If some of the bound
+ // arguments are stored by value or rvalue reference, we move them.
+ return functional_internal::Apply<R>(absl::move(bound_args_), Idx(),
+ absl::forward<FreeArgs>(free_args)...);
+ }
+};
+
+template <class F, class... BoundArgs>
+using bind_front_t = FrontBinder<decay_t<F>, absl::decay_t<BoundArgs>...>;
+
+} // namespace functional_internal
+ABSL_NAMESPACE_END
+} // namespace absl
+
+#endif // ABSL_FUNCTIONAL_INTERNAL_FRONT_BINDER_H_
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