Introduce rtc::Maybe<T>, which either contains a T or not.

webrtc/base/maybe_unittest.cc

Index: webrtc/base/maybe_unittest.cc
diff --git a/webrtc/base/maybe_unittest.cc b/webrtc/base/maybe_unittest.cc
new file mode 100644
index 0000000000000000000000000000000000000000..e2b8df70459bd581184df92f659f7f2e78bca4f8
--- /dev/null
+++ b/webrtc/base/maybe_unittest.cc
@@ -0,0 +1,455 @@
+/*
+ *  Copyright 2015 The WebRTC Project Authors. All rights reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include <sstream>
+#include <string>
+#include <utility>
+#include <vector>
+
+#include "webrtc/base/gunit.h"
+#include "webrtc/base/maybe.h"
+
+namespace rtc {
+
+namespace {
+
+// Class whose instances logs various method calls (constructor, destructor,
+// etc.). Each instance has a unique ID (a simple global sequence number) and
+// an origin ID. When a copy is made, the new object gets a fresh ID but copies
+// the origin ID from the original. When a new Logger is created from scratch,
+// it gets a fresh ID, and the origin ID is the same as the ID (default
+// constructor) or given as an argument (explicit constructor).
+class Logger {
+ public:
+  Logger() : id_(next_id_++), origin_(id_) { Log("default constructor"); }
+  explicit Logger(int origin) : id_(next_id_++), origin_(origin) {
+    Log("explicit constructor");
+  }
+  Logger(const Logger& other) : id_(next_id_++), origin_(other.origin_) {
+    LogFrom("copy constructor", other);
+  }
+  Logger(Logger&& other) : id_(next_id_++), origin_(other.origin_) {
+    LogFrom("move constructor", other);
+  }
+  ~Logger() { Log("destructor"); }
+  Logger& operator=(const Logger& other) {
+    origin_ = other.origin_;
+    LogFrom("operator= copy", other);
+    return *this;
+  }
+  Logger& operator=(Logger&& other) {
+    origin_ = other.origin_;
+    LogFrom("operator= move", other);
+    return *this;
+  }
+  friend void swap(Logger& a, Logger& b) {
+    using std::swap;
+    swap(a.origin_, b.origin_);
+    Log2("swap", a, b);
+  }
+  friend bool operator==(const Logger& a, const Logger& b) {
+    Log2("operator==", a, b);
+    return a.origin_ == b.origin_;
+  }
+  friend bool operator!=(const Logger& a, const Logger& b) {
+    Log2("operator!=", a, b);
+    return a.origin_ != b.origin_;
+  }
+  void Foo() { Log("Foo()"); }
+  void Foo() const { Log("Foo() const"); }
+  static rtc::scoped_ptr<std::vector<std::string>> Setup() {
+    auto s = rtc_make_scoped_ptr(new std::vector<std::string>);
+    Logger::log_ = s.get();
+    Logger::next_id_ = 0;
+    return s;
+  }
+
+ private:
+  int id_;
+  int origin_;
+  static std::vector<std::string>* log_;
+  static int next_id_;
+  void Log(const char* msg) const {
+    std::ostringstream oss;
+    oss << id_ << ':' << origin_ << ". " << msg;
+    log_->push_back(oss.str());
+  }
+  void LogFrom(const char* msg, const Logger& other) const {
+    std::ostringstream oss;
+    oss << id_ << ':' << origin_ << ". " << msg << " (from " << other.id_ << ':'
+        << other.origin_ << ")";
+    log_->push_back(oss.str());
+  }
+  static void Log2(const char* msg, const Logger& a, const Logger& b) {
+    std::ostringstream oss;
+    oss << msg << ' ' << a.id_ << ':' << a.origin_ << ", " << b.id_ << ':'
+        << b.origin_;
+    log_->push_back(oss.str());
+  }
+};
+
+std::vector<std::string>* Logger::log_ = nullptr;
+int Logger::next_id_ = 0;
+
+// Append all the other args to the vector pointed to by the first arg.
+template <typename T>
+void VectorAppend(std::vector<T>* v) {}
+template <typename T, typename... Ts>
+void VectorAppend(std::vector<T>* v, const T& e, Ts... es) {
+  v->push_back(e);
+  VectorAppend(v, es...);
+}
+
+// Create a vector of strings. Because we're not allowed to use
+// std::initializer_list.
+template <typename... Ts>
+std::vector<std::string> V(Ts... es) {
+  std::vector<std::string> strings;
+  VectorAppend(&strings, static_cast<std::string>(es)...);
+  return strings;
+}
+
+}  // namespace
+
+TEST(MaybeTest, TestConstructDefault) {
+  auto log = Logger::Setup();
+  {
+    Maybe<Logger> x;
+    EXPECT_FALSE(x);
+  }
+  EXPECT_EQ(V("0:0. default constructor", "0:0. destructor"), *log);
+}
+
+TEST(MaybeTest, TestConstructCopyEmpty) {
+  auto log = Logger::Setup();
+  {
+    Maybe<Logger> x;
+    EXPECT_FALSE(x);
+    auto y = x;
+    EXPECT_FALSE(y);
+  }
+  EXPECT_EQ(V("0:0. default constructor", "1:0. copy constructor (from 0:0)",
+              "1:0. destructor", "0:0. destructor"),
+            *log);
+}
+
+TEST(MaybeTest, TestConstructCopyFull) {
+  auto log = Logger::Setup();
+  {
+    Logger a;
+    Maybe<Logger> x(a);
+    EXPECT_TRUE(x);
+    log->push_back("---");
+    auto y = x;
+    EXPECT_TRUE(y);
+    log->push_back("---");
+  }
+  EXPECT_EQ(V("0:0. default constructor", "1:0. copy constructor (from 0:0)",
+              "---", "2:0. copy constructor (from 1:0)", "---",
+              "2:0. destructor", "1:0. destructor", "0:0. destructor"),
+            *log);
+}
+
+TEST(MaybeTest, TestConstructMoveEmpty) {
+  auto log = Logger::Setup();
+  {
+    Maybe<Logger> x;
+    EXPECT_FALSE(x);
+    auto y = static_cast<Maybe<Logger>&&>(x);
+    EXPECT_FALSE(y);
+  }
+  EXPECT_EQ(V("0:0. default constructor", "1:0. move constructor (from 0:0)",
+              "1:0. destructor", "0:0. destructor"),
+            *log);
+}
+
+TEST(MaybeTest, TestConstructMoveFull) {
+  auto log = Logger::Setup();
+  {
+    Maybe<Logger> x(Logger(17));
+    EXPECT_TRUE(x);
+    log->push_back("---");
+    auto y = static_cast<Maybe<Logger>&&>(x);
+    EXPECT_TRUE(x);
+    EXPECT_TRUE(y);
+    log->push_back("---");
+  }
+  EXPECT_EQ(
+      V("0:17. explicit constructor", "1:17. move constructor (from 0:17)",
+        "0:17. destructor", "---", "2:17. move constructor (from 1:17)", "---",
+        "2:17. destructor", "1:17. destructor"),
+      *log);
+}
+
+TEST(MaybeTest, TestCopyAssignToEmptyFromEmpty) {
+  auto log = Logger::Setup();
+  {
+    Maybe<Logger> x, y;
+    x = y;
+  }
+  EXPECT_EQ(
+      V("0:0. default constructor", "1:1. default constructor",
+        "0:1. operator= copy (from 1:1)", "1:1. destructor", "0:1. destructor"),
+      *log);
+}
+
+TEST(MaybeTest, TestCopyAssignToFullFromEmpty) {
+  auto log = Logger::Setup();
+  {
+    Maybe<Logger> x(Logger(17));
+    Maybe<Logger> y;
+    log->push_back("---");
+    x = y;
+    log->push_back("---");
+  }
+  EXPECT_EQ(
+      V("0:17. explicit constructor", "1:17. move constructor (from 0:17)",
+        "0:17. destructor", "2:2. default constructor", "---",
+        "1:2. operator= copy (from 2:2)", "---", "2:2. destructor",
+        "1:2. destructor"),
+      *log);
+}
+
+TEST(MaybeTest, TestCopyAssignToEmptyFromFull) {
+  auto log = Logger::Setup();
+  {
+    Maybe<Logger> x;
+    Maybe<Logger> y(Logger(17));
+    log->push_back("---");
+    x = y;
+    log->push_back("---");
+  }
+  EXPECT_EQ(V("0:0. default constructor", "1:17. explicit constructor",
+              "2:17. move constructor (from 1:17)", "1:17. destructor", "---",
+              "0:17. operator= copy (from 2:17)", "---", "2:17. destructor",
+              "0:17. destructor"),
+            *log);
+}
+
+TEST(MaybeTest, TestCopyAssignToFullFromFull) {
+  auto log = Logger::Setup();
+  {
+    Maybe<Logger> x(Logger(17));
+    Maybe<Logger> y(Logger(42));
+    log->push_back("---");
+    x = y;
+    log->push_back("---");
+  }
+  EXPECT_EQ(
+      V("0:17. explicit constructor", "1:17. move constructor (from 0:17)",
+        "0:17. destructor", "2:42. explicit constructor",
+        "3:42. move constructor (from 2:42)", "2:42. destructor", "---",
+        "1:42. operator= copy (from 3:42)", "---", "3:42. destructor",
+        "1:42. destructor"),
+      *log);
+}
+
+TEST(MaybeTest, TestCopyAssignToEmptyFromT) {
+  auto log = Logger::Setup();
+  {
+    Maybe<Logger> x;
+    Logger y(17);
+    log->push_back("---");
+    x = y;
+    log->push_back("---");
+  }
+  EXPECT_EQ(V("0:0. default constructor", "1:17. explicit constructor", "---",
+              "0:17. operator= copy (from 1:17)", "---", "1:17. destructor",
+              "0:17. destructor"),
+            *log);
+}
+
+TEST(MaybeTest, TestCopyAssignToFullFromT) {
+  auto log = Logger::Setup();
+  {
+    Maybe<Logger> x(Logger(17));
+    Logger y(42);
+    log->push_back("---");
+    x = y;
+    log->push_back("---");
+  }
+  EXPECT_EQ(
+      V("0:17. explicit constructor", "1:17. move constructor (from 0:17)",
+        "0:17. destructor", "2:42. explicit constructor", "---",
+        "1:42. operator= copy (from 2:42)", "---", "2:42. destructor",
+        "1:42. destructor"),
+      *log);
+}
+
+TEST(MaybeTest, TestMoveAssignToEmptyFromEmpty) {
+  auto log = Logger::Setup();
+  {
+    Maybe<Logger> x, y;
+    x = static_cast<Maybe<Logger>&&>(y);
+  }
+  EXPECT_EQ(
+      V("0:0. default constructor", "1:1. default constructor",
+        "0:1. operator= move (from 1:1)", "1:1. destructor", "0:1. destructor"),
+      *log);
+}
+
+TEST(MaybeTest, TestMoveAssignToFullFromEmpty) {
+  auto log = Logger::Setup();
+  {
+    Maybe<Logger> x(Logger(17));
+    Maybe<Logger> y;
+    log->push_back("---");
+    x = static_cast<Maybe<Logger>&&>(y);
+    log->push_back("---");
+  }
+  EXPECT_EQ(
+      V("0:17. explicit constructor", "1:17. move constructor (from 0:17)",
+        "0:17. destructor", "2:2. default constructor", "---",
+        "1:2. operator= move (from 2:2)", "---", "2:2. destructor",
+        "1:2. destructor"),
+      *log);
+}
+
+TEST(MaybeTest, TestMoveAssignToEmptyFromFull) {
+  auto log = Logger::Setup();
+  {
+    Maybe<Logger> x;
+    Maybe<Logger> y(Logger(17));
+    log->push_back("---");
+    x = static_cast<Maybe<Logger>&&>(y);
+    log->push_back("---");
+  }
+  EXPECT_EQ(V("0:0. default constructor", "1:17. explicit constructor",
+              "2:17. move constructor (from 1:17)", "1:17. destructor", "---",
+              "0:17. operator= move (from 2:17)", "---", "2:17. destructor",
+              "0:17. destructor"),
+            *log);
+}
+
+TEST(MaybeTest, TestMoveAssignToFullFromFull) {
+  auto log = Logger::Setup();
+  {
+    Maybe<Logger> x(Logger(17));
+    Maybe<Logger> y(Logger(42));
+    log->push_back("---");
+    x = static_cast<Maybe<Logger>&&>(y);
+    log->push_back("---");
+  }
+  EXPECT_EQ(
+      V("0:17. explicit constructor", "1:17. move constructor (from 0:17)",
+        "0:17. destructor", "2:42. explicit constructor",
+        "3:42. move constructor (from 2:42)", "2:42. destructor", "---",
+        "1:42. operator= move (from 3:42)", "---", "3:42. destructor",
+        "1:42. destructor"),
+      *log);
+}
+
+TEST(MaybeTest, TestMoveAssignToEmptyFromT) {
+  auto log = Logger::Setup();
+  {
+    Maybe<Logger> x;
+    Logger y(17);
+    log->push_back("---");
+    x = static_cast<Logger&&>(y);
+    log->push_back("---");
+  }
+  EXPECT_EQ(V("0:0. default constructor", "1:17. explicit constructor", "---",
+              "0:17. operator= move (from 1:17)", "---", "1:17. destructor",
+              "0:17. destructor"),
+            *log);
+}
+
+TEST(MaybeTest, TestMoveAssignToFullFromT) {
+  auto log = Logger::Setup();
+  {
+    Maybe<Logger> x(Logger(17));
+    Logger y(42);
+    log->push_back("---");
+    x = static_cast<Logger&&>(y);
+    log->push_back("---");
+  }
+  EXPECT_EQ(
+      V("0:17. explicit constructor", "1:17. move constructor (from 0:17)",
+        "0:17. destructor", "2:42. explicit constructor", "---",
+        "1:42. operator= move (from 2:42)", "---", "2:42. destructor",
+        "1:42. destructor"),
+      *log);
+}
+
+TEST(MaybeTest, TestDereference) {
+  auto log = Logger::Setup();
+  {
+    Maybe<Logger> x(Logger(42));
+    const auto& y = x;
+    log->push_back("---");
+    x->Foo();
+    y->Foo();
+    static_cast<Maybe<Logger>&&>(x)->Foo();
+    static_cast<const Maybe<Logger>&&>(y)->Foo();
+    log->push_back("---");
+    (*x).Foo();
+    (*y).Foo();
+    (*static_cast<Maybe<Logger>&&>(x)).Foo();
+    (*static_cast<const Maybe<Logger>&&>(y)).Foo();
+    log->push_back("---");
+  }
+  EXPECT_EQ(V("0:42. explicit constructor",
+              "1:42. move constructor (from 0:42)", "0:42. destructor", "---",
+              "1:42. Foo()", "1:42. Foo() const", "1:42. Foo()",
+              "1:42. Foo() const", "---", "1:42. Foo()", "1:42. Foo() const",
+              "1:42. Foo()", "1:42. Foo() const", "---", "1:42. destructor"),
+            *log);
+}
+
+TEST(MaybeTest, TestEquality) {
+  auto log = Logger::Setup();
+  {
+    Logger a(17), b(42);
+    Maybe<Logger> ma1(a), ma2(a), mb(b), me1, me2;
+    log->push_back("---");
+    EXPECT_EQ(ma1, ma1);
+    EXPECT_EQ(ma1, ma2);
+    EXPECT_NE(ma1, mb);
+    EXPECT_NE(ma1, me1);
+    EXPECT_EQ(me1, me1);
+    EXPECT_EQ(me1, me2);
+    log->push_back("---");
+  }
+  EXPECT_EQ(V("0:17. explicit constructor", "1:42. explicit constructor",
+              "2:17. copy constructor (from 0:17)",
+              "3:17. copy constructor (from 0:17)",
+              "4:42. copy constructor (from 1:42)", "5:5. default constructor",
+              "6:6. default constructor", "---", "operator== 2:17, 2:17",
+              "operator== 2:17, 3:17", "operator!= 2:17, 4:42", "---",
+              "6:6. destructor", "5:5. destructor", "4:42. destructor",
+              "3:17. destructor", "2:17. destructor", "1:42. destructor",
+              "0:17. destructor"),
+            *log);
+}
+
+TEST(MaybeTest, TestSwap) {
+  auto log = Logger::Setup();
+  {
+    Logger a(17), b(42);
+    Maybe<Logger> x1(a), x2(b), y1(a), y2, z1, z2;
+    log->push_back("---");
+    swap(x1, x2);  // Swap full <-> full.
+    swap(y1, y2);  // Swap full <-> empty.
+    swap(z1, z2);  // Swap empty <-> empty.
+    log->push_back("---");
+  }
+  EXPECT_EQ(V("0:17. explicit constructor", "1:42. explicit constructor",
+              "2:17. copy constructor (from 0:17)",
+              "3:42. copy constructor (from 1:42)",
+              "4:17. copy constructor (from 0:17)", "5:5. default constructor",
+              "6:6. default constructor", "7:7. default constructor", "---",
+              "swap 2:42, 3:17", "swap 4:5, 5:17", "swap 6:7, 7:6", "---",
+              "7:6. destructor", "6:7. destructor", "5:17. destructor",
+              "4:5. destructor", "3:17. destructor", "2:42. destructor",
+              "1:42. destructor", "0:17. destructor"),
+            *log);
+}
+
+}  // namespace rtc