[base] Add a lightweight function wrapper - function_ref
This class is supposed to land in C++23, and allows for a much
more performant passing of generic callbacks. It's a non-owning
view of a function, similar to what string_view is to string.
What this means is one has to be careful when using it to never
create a dangling reference.
The best use case is passing a callback into some function that
is going to use it and never stores it for later.
Bug: 180535478
Test: atest libbase_test
Change-Id: I9ddd31cc6bcd012bf157f5f8215802426593530c
diff --git a/function_ref_test.cpp b/function_ref_test.cpp
new file mode 100644
index 0000000..44194f7
--- /dev/null
+++ b/function_ref_test.cpp
@@ -0,0 +1,87 @@
+/*
+ * Copyright (C) 2021 The Android Open Source Project
+ *
+ * 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.
+ */
+
+#include "android-base/function_ref.h"
+
+#include <gtest/gtest.h>
+
+#include <functional>
+#include <string>
+
+namespace android::base {
+
+TEST(function_ref, Ctor) {
+ // Making sure it can be constructed in all meaningful ways
+
+ using EmptyFunc = function_ref<void()>;
+
+ EmptyFunc f1([] {});
+
+ struct Functor {
+ void operator()() const {}
+ };
+ EmptyFunc f2(Functor{});
+ Functor fctr;
+ EmptyFunc f3(fctr);
+
+ EmptyFunc f4(std::function<void()>([f1, f2, f3] {
+ (void)f1;
+ (void)f2;
+ (void)f3;
+ }));
+
+ const std::function<void()> func = [] {};
+ EmptyFunc f5(func);
+
+ static_assert(sizeof(f1) <= 2 * sizeof(void*), "Too big function_ref");
+ static_assert(sizeof(f2) <= 2 * sizeof(void*), "Too big function_ref");
+ static_assert(sizeof(f3) <= 2 * sizeof(void*), "Too big function_ref");
+ static_assert(sizeof(f4) <= 2 * sizeof(void*), "Too big function_ref");
+ static_assert(sizeof(f5) <= 2 * sizeof(void*), "Too big function_ref");
+}
+
+TEST(function_ref, Call) {
+ function_ref<int(int)> view = [](int i) { return i + 1; };
+ EXPECT_EQ(1, view(0));
+ EXPECT_EQ(-1, view(-2));
+
+ function_ref<std::string(std::string)> fs = [](const std::string& s) { return s + "1"; };
+ EXPECT_STREQ("s1", fs("s").c_str());
+ EXPECT_STREQ("ssss1", fs("ssss").c_str());
+
+ std::string base;
+ auto lambda = [&base]() { return base + "1"; };
+ function_ref<std::string()> fs2 = lambda;
+ base = "one";
+ EXPECT_STREQ("one1", fs2().c_str());
+ base = "forty two";
+ EXPECT_STREQ("forty two1", fs2().c_str());
+}
+
+TEST(function_ref, CopyAndAssign) {
+ function_ref<int(int)> view = [](int i) { return i + 1; };
+ EXPECT_EQ(1, view(0));
+ view = [](int i) { return i - 1; };
+ EXPECT_EQ(0, view(1));
+
+ function_ref<int(int)> view2 = view;
+ EXPECT_EQ(view(10), view2(10));
+
+ view = view2;
+ EXPECT_EQ(view(10), view2(10));
+}
+
+} // namespace android::base