[ADT] Add make_scope_exit().

Summary: make_scope_exit() is described in C++ proposal p0052r2, which uses RAII to do cleanup works at scope exit.

Reviewers: chandlerc

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D22796

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@278251 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/ADT/ScopeExit.h

@@ -0,0 +1,55 @@
+//===- llvm/ADT/ScopeExit.h - Execute code at scope exit --------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines the make_scope_exit function, which executes user-defined
+// cleanup logic at scope exit.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ADT_SCOPE_EXIT_H
+#define LLVM_ADT_SCOPE_EXIT_H
+
+#include "llvm/Support/Compiler.h"
+
+#include <type_traits>
+#include <utility>
+
+namespace llvm {
+namespace detail {
+
+template <typename Callable> class LLVM_ATTRIBUTE_UNUSED_RESULT scope_exit {
+  Callable ExitFunction;
+
+public:
+  template <typename Fp>
+  explicit scope_exit(Fp &&F) : ExitFunction(std::forward<Fp>(F)) {}
+
+  scope_exit(const scope_exit &) = default;
+  scope_exit(scope_exit &&) = default;
+
+  ~scope_exit() { ExitFunction(); }
+};
+
+} // end namespace detail
+
+// Keeps the callable object that is passed in, and execute it at the
+// destruction of the returned object (usually at the scope exit where the
+// returned object is kept).
+//
+// Interface is specified by p0052r2.
+template <typename Callable>
+detail::scope_exit<typename std::decay<Callable>::type>
+make_scope_exit(Callable &&F) {
+  return detail::scope_exit<typename std::decay<Callable>::type>(
+      std::forward<Callable>(F));
+}
+
+} // end namespace llvm
+
+#endif

unittests/ADT/CMakeLists.txt

@@ -34,6 +34,7 @@ set(ADTSources
   PriorityWorklistTest.cpp
   RangeAdapterTest.cpp
   SCCIteratorTest.cpp
+  ScopeExitTest.cpp
   SequenceTest.cpp
   SetVectorTest.cpp
   SmallPtrSetTest.cpp

unittests/ADT/ScopeExitTest.cpp

@@ -0,0 +1,32 @@
+//===- llvm/unittest/ADT/ScopeExit.cpp - Scope exit unit tests --*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/ScopeExit.h"
+#include "gtest/gtest.h"
+
+using namespace llvm;
+
+namespace {
+
+TEST(ScopeExitTest, Basic) {
+  struct Callable {
+    bool &Called;
+    Callable(bool &Called) : Called(Called) {}
+    Callable(Callable &&RHS) : Called(RHS.Called) {}
+    void operator()() { Called = true; }
+  };
+  bool Called = false;
+  {
+    auto g = make_scope_exit(Callable(Called));
+    EXPECT_FALSE(Called);
+  }
+  EXPECT_TRUE(Called);
+}
+
+} // end anonymous namespace