Add a polymorphic_ptr<T> smart pointer data type. It's a somewhat silly

unique ownership smart pointer which is *deep* copyable by assuming it
can call a T::clone() method to allocate a copy of the owned data.

This is mostly useful with containers or other collections of uniquely
owned data in C++98 where they *might* copy. With C++11 we can likely
remove this in favor of move-only types and containers wrapped around
those types.

llvm-svn: 194315

llvm/include/llvm/ADT/polymorphic_ptr.h

+//===- llvm/ADT/polymorphic_ptr.h - Smart copyable owned ptr ----*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+/// \file
+/// This file provides a polymorphic_ptr class template. See the class comments
+/// for details about this API, its intended use cases, etc.
+///
+/// The primary motivation here is to work around the necessity of copy
+/// semantics in C++98. This is typically used where any actual copies are
+/// incidental or unnecessary. As a consequence, it is expected to cease to be
+/// useful and be removed when we can directly rely on move-only types.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ADT_POLYMORPHIC_PTR_H
+#define LLVM_ADT_POLYMORPHIC_PTR_H
+
+#include "llvm/Support/Compiler.h"
+
+namespace llvm {
+
+/// \brief An owning, copyable polymorphic smart pointer.
+///
+/// This pointer exists to provide copyable owned smart pointer. Rather than
+/// shared ownership semantics, it has unique ownership semantics and deep copy
+/// semantics. It is copyable by requiring that the underlying type exposes
+/// a method which can produce a (heap allocated) clone.
+///
+/// Note that in almost all scenarios use of this could be avoided if we could
+/// build move-only containers of a std::unique_ptr, but until then this
+/// provides an effective way to place polymorphic objects in a container.
+template <typename T> class polymorphic_ptr {
+  T *ptr;
+
+public:
+  explicit polymorphic_ptr(T *ptr = 0) : ptr(ptr) {}
+  polymorphic_ptr(const polymorphic_ptr &arg) : ptr(arg->clone()) {}
+#if LLVM_HAS_RVALUE_REFERENCES
+  polymorphic_ptr(polymorphic_ptr &&arg) : ptr(arg.take()) {}
+#endif
+  ~polymorphic_ptr() { delete ptr; }
+
+  polymorphic_ptr &operator=(polymorphic_ptr arg) {
+    swap(arg);
+    return *this;
+  }
+  polymorphic_ptr &operator=(T *arg) {
+    if (arg != ptr) {
+      delete ptr;
+      ptr = arg;
+    }
+    return *this;
+  }
+
+  T &operator*() const { return *ptr; }
+  T *operator->() const { return ptr; }
+  LLVM_EXPLICIT operator bool() const { return ptr != 0; }
+  bool operator!() const { return ptr == 0; }
+
+  T *get() const { return ptr; }
+
+  T *take() {
+    T *tmp = ptr;
+    ptr = 0;
+    return tmp;
+  }
+
+  void swap(polymorphic_ptr &arg) {
+    T *tmp = ptr;
+    ptr = arg.ptr;
+    arg.ptr = tmp;
+  }
+};
+
+template <typename T>
+void swap(polymorphic_ptr<T> &lhs, polymorphic_ptr<T> &rhs) {
+  lhs.swap(rhs);
+}
+
+template <typename T, typename U>
+bool operator==(const polymorphic_ptr<T> &lhs, const polymorphic_ptr<U> &rhs) {
+  return lhs.get() == rhs.get();
+}
+
+template <typename T, typename U>
+bool operator!=(const polymorphic_ptr<T> &lhs, const polymorphic_ptr<U> &rhs) {
+  return lhs.get() != rhs.get();
+}
+
+template <typename T, typename U>
+bool operator==(const polymorphic_ptr<T> &lhs, U *rhs) {
+  return lhs.get() == rhs;
+}
+
+template <typename T, typename U>
+bool operator!=(const polymorphic_ptr<T> &lhs, U *rhs) {
+  return lhs.get() != rhs;
+}
+
+template <typename T, typename U>
+bool operator==(T *lhs, const polymorphic_ptr<U> &rhs) {
+  return lhs == rhs.get();
+}
+
+template <typename T, typename U>
+bool operator!=(T *lhs, const polymorphic_ptr<U> &rhs) {
+  return lhs != rhs.get();
+}
+
+}
+
+#endif

llvm/unittests/ADT/CMakeLists.txt

@@ -35,6 +35,7 @@ set(ADTSources
   TripleTest.cpp
   TwineTest.cpp
   VariadicFunctionTest.cpp
+  polymorphic_ptr_test.cpp
  )
 
 # They cannot be compiled on MSVC9 due to its bug.

llvm/unittests/ADT/polymorphic_ptr_test.cpp

+//===- llvm/unittest/ADT/polymorphic_ptr.h - polymorphic_ptr<T> tests -----===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "gtest/gtest.h"
+#include "llvm/ADT/polymorphic_ptr.h"
+#include "llvm/Support/raw_ostream.h"
+
+using namespace llvm;
+
+namespace {
+
+TEST(polymorphic_ptr_test, Basic) {
+  struct S {
+    S(int x) : x(x) {}
+    int x;
+  };
+
+  polymorphic_ptr<S> null;
+  EXPECT_FALSE((bool)null);
+  EXPECT_TRUE(!null);
+  EXPECT_EQ((S*)0, null.get());
+
+  S *s = new S(42);
+  polymorphic_ptr<S> p(s);
+  EXPECT_TRUE((bool)p);
+  EXPECT_FALSE(!p);
+  EXPECT_TRUE(p != null);
+  EXPECT_FALSE(p == null);
+  EXPECT_TRUE(p == s);
+  EXPECT_TRUE(s == p);
+  EXPECT_FALSE(p != s);
+  EXPECT_FALSE(s != p);
+  EXPECT_EQ(s, &*p);
+  EXPECT_EQ(s, p.operator->());
+  EXPECT_EQ(s, p.get());
+  EXPECT_EQ(42, p->x);
+
+  EXPECT_EQ(s, p.take());
+  EXPECT_FALSE((bool)p);
+  EXPECT_TRUE(!p);
+  p = s;
+  EXPECT_TRUE((bool)p);
+  EXPECT_FALSE(!p);
+  EXPECT_EQ(s, &*p);
+  EXPECT_EQ(s, p.operator->());
+  EXPECT_EQ(s, p.get());
+  EXPECT_EQ(42, p->x);
+
+  polymorphic_ptr<S> p2((llvm_move(p)));
+  EXPECT_FALSE((bool)p);
+  EXPECT_TRUE(!p);
+  EXPECT_TRUE((bool)p2);
+  EXPECT_FALSE(!p2);
+  EXPECT_EQ(s, &*p2);
+
+  using std::swap;
+  swap(p, p2);
+  EXPECT_TRUE((bool)p);
+  EXPECT_FALSE(!p);
+  EXPECT_EQ(s, &*p);
+  EXPECT_FALSE((bool)p2);
+  EXPECT_TRUE(!p2);
+}
+
+}