common: add std::not_fn to backport14.h and unit tests

Signed-off-by: Casey Bodley <cbodley@redhat.com>

diff --git a/src/common/backport14.h b/src/common/backport14.h
index d56e24c3e512f821f32f3fda7edaf2210371a0dd..3e6505d468d31fdfc6afe6da0f75b49ec88b1058 100644 (file)
--- a/src/common/backport14.h
+++ b/src/common/backport14.h
@@ -27,6 +27,8 @@ template<typename T>
 using remove_reference_t = typename std::remove_reference<T>::type;
 template<typename T>
 using result_of_t = typename std::result_of<T>::type;
+template<typename T>
+using decay_t = typename std::decay<T>::type;
 
 namespace _backport14 {
 template<typename T>
@@ -75,10 +77,52 @@ template <typename T, std::size_t N>
 constexpr std::size_t size(const T (&array)[N]) noexcept {
   return N;
 }
+
+/// http://en.cppreference.com/w/cpp/utility/functional/not_fn
+// this implementation uses c++14's result_of_t (above) instead of the c++17
+// invoke_result_t, and so may not behave correctly when SFINAE is required
+template <typename F>
+class not_fn_result {
+  using DecayF = decay_t<F>;
+  DecayF fn;
+ public:
+  explicit not_fn_result(F&& f) : fn(std::forward<F>(f)) {}
+  not_fn_result(not_fn_result&& f) = default;
+  not_fn_result(const not_fn_result& f) = default;
+
+  template<class... Args>
+  auto operator()(Args&&... args) &
+  -> decltype(!std::declval<result_of_t<DecayF&(Args...)>>()) {
+    return !fn(std::forward<Args>(args)...);
+  }
+  template<class... Args>
+  auto operator()(Args&&... args) const&
+  -> decltype(!std::declval<result_of_t<DecayF const&(Args...)>>()) {
+    return !fn(std::forward<Args>(args)...);
+  }
+
+  template<class... Args>
+  auto operator()(Args&&... args) &&
+  -> decltype(!std::declval<result_of_t<DecayF(Args...)>>()) {
+    return !std::move(fn)(std::forward<Args>(args)...);
+  }
+  template<class... Args>
+  auto operator()(Args&&... args) const&&
+  -> decltype(!std::declval<result_of_t<DecayF const(Args...)>>()) {
+    return !std::move(fn)(std::forward<Args>(args)...);
+  }
+};
+
+template <typename F>
+not_fn_result<F> not_fn(F&& fn) {
+  return not_fn_result<F>(std::forward<F>(fn));
+}
+
 } // namespace _backport17
 using _backport14::make_unique;
 using _backport17::size;
 using _backport14::max;
+using _backport17::not_fn;
 } // namespace ceph
 
 #endif // CEPH_COMMON_BACKPORT14_H

diff --git a/src/test/common/CMakeLists.txt b/src/test/common/CMakeLists.txt
index 17034b67aee39b6a758970fdf89014eb69cb1f86..9a2be3df293cc96ca29e8f10b53085086b7b51e9 100644 (file)
--- a/src/test/common/CMakeLists.txt
+++ b/src/test/common/CMakeLists.txt
@@ -271,4 +271,8 @@ add_executable(unittest_iso_8601
     test_iso_8601.cc)
 target_link_libraries(unittest_iso_8601 ceph-common)
 add_ceph_unittest(unittest_iso_8601
-  ${CMAKE_RUNTIME_OUTPUT_DIRECTORY}/unittest_hostname)
+  ${CMAKE_RUNTIME_OUTPUT_DIRECTORY}/unittest_iso_8601)
+
+add_executable(unittest_backport14 test_backport14.cc)
+add_ceph_unittest(unittest_backport14
+  ${CMAKE_RUNTIME_OUTPUT_DIRECTORY}/unittest_backport14)

diff --git a/src/test/common/test_backport14.cc b/src/test/common/test_backport14.cc
new file mode 100644 (file)
index 0000000..63ef5d0
--- /dev/null
+++ b/src/test/common/test_backport14.cc
@@ -0,0 +1,94 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab
+/*
+ * Ceph - scalable distributed file system
+ *
+ * Copyright (C) 2017 Red Hat, Inc.
+ *
+ * Author: Casey Bodley <cbodley@redhat.com>
+ *
+ * This is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License version 2.1, as published by the Free Software
+ * Foundation.  See file COPYING.
+ *
+ */
+
+#include "common/backport14.h" // include first: tests that header is standalone
+#include <gtest/gtest.h>
+
+int int_func() { return 1; }
+bool bool_func0() { return true; }
+bool bool_func1(int a) { return true; }
+bool bool_func2(const std::string& a, int b) { return true; }
+
+// given a callable and argument list, test that the result of ceph::not_fn
+// evaluates to false as both an lvalue and rvalue
+template <typename F, typename ...Args>
+void test_not(F&& fn, Args&&... args)
+{
+  auto res = ceph::not_fn(std::forward<F>(fn));
+  // test res as lvalue
+  EXPECT_FALSE(res(std::forward<Args>(args)...));
+  // test res as rvalue
+  // note: this forwards args twice, but it's okay if none are rvalues
+  EXPECT_FALSE(std::move(res)(std::forward<Args>(args)...));
+}
+
+TEST(Backport14, not_fn)
+{
+  // function pointers
+  test_not(int_func);
+  test_not(&int_func);
+  test_not(bool_func0);
+  test_not(&bool_func0);
+  test_not(bool_func1, 5);
+  test_not(bool_func2, "foo", 5);
+
+  // lambdas
+  auto int_lambda = [] { return 1; };
+  auto bool_lambda0 = [] { return true; };
+  auto bool_lambda1 = [] (int a) { return true; };
+  auto bool_lambda2 = [] (const std::string& a, int b) { return true; };
+
+  test_not(int_lambda);
+  test_not(bool_lambda0);
+  test_not(bool_lambda1, 5);
+  test_not(bool_lambda2, "foo", 5);
+
+  // functors
+  struct int_functor {
+    int operator()() { return 1; }
+  };
+  test_not(int_functor{});
+
+  struct bool_functor {
+    bool operator()() { return true; }
+    bool operator()(int a) { return true; }
+    bool operator()(const std::string& a, int b) { return true; }
+  };
+
+  test_not(bool_functor{});
+  test_not(bool_functor{}, 5);
+  test_not(bool_functor{}, "foo", 5);
+
+  // lvalue-only overload
+  struct lvalue_only_functor {
+    bool operator()() & { return true; } // no overload for rvalue
+  };
+  auto lvalue_result = ceph::not_fn(lvalue_only_functor{});
+  EXPECT_FALSE(lvalue_result());
+  // should not compile:
+  //   EXPECT_FALSE(std::move(lvalue_result)());
+
+  // rvalue-only overload
+  struct rvalue_only_functor {
+    bool operator()() && { return true; } // no overload for lvalue
+  };
+  EXPECT_FALSE(ceph::not_fn(rvalue_only_functor{})());
+  auto lvalue_functor = rvalue_only_functor{};
+  EXPECT_FALSE(ceph::not_fn(lvalue_functor)()); // lvalue functor, rvalue result
+  // should not compile:
+  //   auto lvalue_result2 = ceph::not_fn(rvalue_only_functor{});
+  //   EXPECT_FALSE(lvalue_result2());
+}