C++ mozilla::Some方法代码示例

static bool
TestSomePointerConversion()
{
  Base base;
  Derived derived;

  Maybe<Base*> m1 = Some(&derived);
  MOZ_RELEASE_ASSERT(m1.isSome());
  MOZ_RELEASE_ASSERT(m1);
  MOZ_RELEASE_ASSERT(*m1 == &derived);

  auto m2 = ReturnDerivedPointer();
  MOZ_RELEASE_ASSERT(m2.isSome());
  MOZ_RELEASE_ASSERT(m2);
  MOZ_RELEASE_ASSERT(*m2 == nullptr);

  Maybe<Base*> m3 = Some(&base);
  MOZ_RELEASE_ASSERT(m3.isSome());
  MOZ_RELEASE_ASSERT(m3);
  MOZ_RELEASE_ASSERT(*m3 == &base);

  auto s1 = Some(&derived);
  Maybe<Base*> c1(s1);
  MOZ_RELEASE_ASSERT(c1.isSome());
  MOZ_RELEASE_ASSERT(c1);
  MOZ_RELEASE_ASSERT(*c1 == &derived);

  ExplicitConstructorBasePointer ecbp(Some(&derived));

  return true;
}

Maybe<MaybeCheckTDZ> TDZCheckCache::needsTDZCheck(BytecodeEmitter* bce,
                                                  JSAtom* name) {
  if (!ensureCache(bce)) {
    return Nothing();
  }

  CheckTDZMap::AddPtr p = cache_->lookupForAdd(name);
  if (p) {
    return Some(p->value().wrapped);
  }

  MaybeCheckTDZ rv = CheckTDZ;
  for (TDZCheckCache* it = enclosing(); it; it = it->enclosing()) {
    if (it->cache_) {
      if (CheckTDZMap::Ptr p2 = it->cache_->lookup(name)) {
        rv = p2->value();
        break;
      }
    }
  }

  if (!cache_->add(p, name, rv)) {
    ReportOutOfMemory(bce->cx);
    return Nothing();
  }

  return Some(rv);
}

void UniqueStacks::Stack::AppendFrame(const OnStackFrameKey& aFrame)
{
  // Compute the prefix hash and index before mutating mStack.
  uint32_t prefixHash = mStack.Hash();
  uint32_t prefix = mUniqueStacks.GetOrAddStackIndex(mStack);
  mStack.mPrefixHash = Some(prefixHash);
  mStack.mPrefix = Some(prefix);
  mStack.mFrame = mUniqueStacks.GetOrAddFrameIndex(aFrame);
}

static bool
TestApply()
{
  // Check that apply handles the 'Nothing' case.
  gFunctionWasApplied = false;
  Maybe<BasicValue> mayValue;
  mayValue.apply(&IncrementTag);
  mayValue.apply(&AccessValue);
  mayValue.apply(&IncrementTagBy, 1);
  mayValue.apply(&AccessValueWithArg, 1);
  MOZ_RELEASE_ASSERT(!gFunctionWasApplied);

  // Check that apply handles the 'Some' case.
  mayValue = Some(BasicValue(1));
  mayValue.apply(&IncrementTag);
  MOZ_RELEASE_ASSERT(gFunctionWasApplied);
  MOZ_RELEASE_ASSERT(mayValue->GetTag() == 2);
  gFunctionWasApplied = false;
  mayValue.apply(&AccessValue);
  MOZ_RELEASE_ASSERT(gFunctionWasApplied);
  gFunctionWasApplied = false;
  mayValue.apply(&IncrementTagBy, 2);
  MOZ_RELEASE_ASSERT(gFunctionWasApplied);
  MOZ_RELEASE_ASSERT(mayValue->GetTag() == 4);
  gFunctionWasApplied = false;
  mayValue.apply(&AccessValueWithArg, 1);
  MOZ_RELEASE_ASSERT(gFunctionWasApplied);

  // Check that apply works with a const reference.
  const Maybe<BasicValue>& mayValueCRef = mayValue;
  gFunctionWasApplied = false;
  mayValueCRef.apply(&AccessValue);
  MOZ_RELEASE_ASSERT(gFunctionWasApplied);
  gFunctionWasApplied = false;
  mayValueCRef.apply(&AccessValueWithArg, 1);
  MOZ_RELEASE_ASSERT(gFunctionWasApplied);

  // Check that apply works with functors.
  IncrementTagFunctor tagIncrementer;
  MOZ_RELEASE_ASSERT(tagIncrementer.mBy.GetStatus() == eWasConstructed);
  mayValue = Some(BasicValue(1));
  mayValue.apply(tagIncrementer);
  MOZ_RELEASE_ASSERT(mayValue->GetTag() == 2);
  MOZ_RELEASE_ASSERT(tagIncrementer.mBy.GetStatus() == eWasConstructed);
  mayValue.apply(tagIncrementer, BasicValue(2));
  MOZ_RELEASE_ASSERT(mayValue->GetTag() == 4);
  MOZ_RELEASE_ASSERT(tagIncrementer.mBy.GetStatus() == eWasConstructed);
  MOZ_RELEASE_ASSERT(tagIncrementer.mArgMoved == true);
  BasicValue incrementBy(3);
  mayValue.apply(tagIncrementer, incrementBy);
  MOZ_RELEASE_ASSERT(mayValue->GetTag() == 7);
  MOZ_RELEASE_ASSERT(tagIncrementer.mBy.GetStatus() == eWasConstructed);
  MOZ_RELEASE_ASSERT(tagIncrementer.mArgMoved == false);

  return true;
}

static bool
TestMap()
{
  // Check that map handles the 'Nothing' case.
  Maybe<BasicValue> mayValue;
  MOZ_RELEASE_ASSERT(mayValue.map(&TimesTwo) == Nothing());
  static_assert(IsSame<Maybe<int>,
                       DECLTYPE(mayValue.map(&TimesTwo))>::value,
                "map(TimesTwo) should return a Maybe<int>");
  MOZ_RELEASE_ASSERT(mayValue.map(&TimesTwoAndResetOriginal) == Nothing());

  // Check that map handles the 'Some' case.
  mayValue = Some(BasicValue(2));
  MOZ_RELEASE_ASSERT(mayValue.map(&TimesTwo) == Some(4));
  MOZ_RELEASE_ASSERT(mayValue.map(&TimesTwoAndResetOriginal) == Some(4));
  MOZ_RELEASE_ASSERT(mayValue->GetTag() == 1);
  mayValue = Some(BasicValue(2));

  // Check that map works with a const reference.
  mayValue->SetTag(2);
  const Maybe<BasicValue>& mayValueCRef = mayValue;
  MOZ_RELEASE_ASSERT(mayValueCRef.map(&TimesTwo) == Some(4));
  static_assert(IsSame<Maybe<int>,
                       DECLTYPE(mayValueCRef.map(&TimesTwo))>::value,
                "map(TimesTwo) should return a Maybe<int>");

  // Check that map works with functors.
  MultiplyTagFunctor tagMultiplier;
  MOZ_RELEASE_ASSERT(tagMultiplier.mBy.GetStatus() == eWasConstructed);
  MOZ_RELEASE_ASSERT(mayValue.map(tagMultiplier) == Some(4));
  MOZ_RELEASE_ASSERT(tagMultiplier.mBy.GetStatus() == eWasConstructed);

  // Check that map works with lambda expressions.
  int two = 2;
  mayValue = Some(BasicValue(2));
  Maybe<int> mappedValue =
    mayValue.map([&](const BasicValue& aVal) {
      return aVal.GetTag() * two;
    });
  MOZ_RELEASE_ASSERT(mappedValue == Some(4));
  mappedValue =
    mayValue.map([=](const BasicValue& aVal) {
      return aVal.GetTag() * two;
    });
  MOZ_RELEASE_ASSERT(mappedValue == Some(4));
  mappedValue =
    mayValueCRef.map([&](const BasicValue& aVal) {
      return aVal.GetTag() * two;
    });
  MOZ_RELEASE_ASSERT(mappedValue == Some(4));

  return true;
}

static bool
TestMap()
{
  // Check that map handles the 'Nothing' case.
  Maybe<BasicValue> mayValue;
  MOZ_RELEASE_ASSERT(mayValue.map(&TimesTwo) == Nothing());
  static_assert(IsSame<Maybe<int>,
                       DECLTYPE(mayValue.map(&TimesTwo))>::value,
                "map(TimesTwo) should return a Maybe<int>");
  MOZ_RELEASE_ASSERT(mayValue.map(&TimesTwoAndResetOriginal) == Nothing());
  MOZ_RELEASE_ASSERT(mayValue.map(&TimesNum, 3) == Nothing());
  static_assert(IsSame<Maybe<int>,
                       DECLTYPE(mayValue.map(&TimesNum, 3))>::value,
                "map(TimesNum, 3) should return a Maybe<int>");
  MOZ_RELEASE_ASSERT(mayValue.map(&TimesNumAndResetOriginal, 3) == Nothing());

  // Check that map handles the 'Some' case.
  mayValue = Some(BasicValue(2));
  MOZ_RELEASE_ASSERT(mayValue.map(&TimesTwo) == Some(4));
  MOZ_RELEASE_ASSERT(mayValue.map(&TimesTwoAndResetOriginal) == Some(4));
  MOZ_RELEASE_ASSERT(mayValue->GetTag() == 1);
  mayValue = Some(BasicValue(2));
  MOZ_RELEASE_ASSERT(mayValue.map(&TimesNum, 3) == Some(6));
  MOZ_RELEASE_ASSERT(mayValue.map(&TimesNumAndResetOriginal, 3) == Some(6));
  MOZ_RELEASE_ASSERT(mayValue->GetTag() == 1);

  // Check that map works with a const reference.
  mayValue->SetTag(2);
  const Maybe<BasicValue>& mayValueCRef = mayValue;
  MOZ_RELEASE_ASSERT(mayValueCRef.map(&TimesTwo) == Some(4));
  static_assert(IsSame<Maybe<int>,
                       DECLTYPE(mayValueCRef.map(&TimesTwo))>::value,
                "map(TimesTwo) should return a Maybe<int>");
  MOZ_RELEASE_ASSERT(mayValueCRef.map(&TimesNum, 3) == Some(6));
  static_assert(IsSame<Maybe<int>,
                       DECLTYPE(mayValueCRef.map(&TimesNum, 3))>::value,
                "map(TimesNum, 3) should return a Maybe<int>");

  // Check that map works with functors.
  // XXX(seth): Support for functors will be added in bug 1054115; it had to be
  // ripped out temporarily because of incompatibilities with GCC 4.4.
  /*
  MultiplyTagFunctor tagMultiplier;
  MOZ_RELEASE_ASSERT(tagMultiplier.mBy.GetStatus() == eWasConstructed);
  MOZ_RELEASE_ASSERT(mayValue.map(tagMultiplier) == Some(4));
  MOZ_RELEASE_ASSERT(tagMultiplier.mBy.GetStatus() == eWasConstructed);
  MOZ_RELEASE_ASSERT(mayValue.map(tagMultiplier, BasicValue(3)) == Some(6));
  MOZ_RELEASE_ASSERT(tagMultiplier.mBy.GetStatus() == eWasConstructed);
  MOZ_RELEASE_ASSERT(tagMultiplier.mArgMoved == true);
  BasicValue multiplyBy(3);
  MOZ_RELEASE_ASSERT(mayValue.map(tagMultiplier, multiplyBy) == Some(6));
  MOZ_RELEASE_ASSERT(tagMultiplier.mBy.GetStatus() == eWasConstructed);
  MOZ_RELEASE_ASSERT(tagMultiplier.mArgMoved == false);
  */

  return true;
}

static bool
TestApply()
{
  // Check that apply handles the 'Nothing' case.
  gFunctionWasApplied = false;
  Maybe<BasicValue> mayValue;
  mayValue.apply(&IncrementTag);
  mayValue.apply(&AccessValue);
  MOZ_RELEASE_ASSERT(!gFunctionWasApplied);

  // Check that apply handles the 'Some' case.
  mayValue = Some(BasicValue(1));
  mayValue.apply(&IncrementTag);
  MOZ_RELEASE_ASSERT(gFunctionWasApplied);
  MOZ_RELEASE_ASSERT(mayValue->GetTag() == 2);
  gFunctionWasApplied = false;
  mayValue.apply(&AccessValue);
  MOZ_RELEASE_ASSERT(gFunctionWasApplied);

  // Check that apply works with a const reference.
  const Maybe<BasicValue>& mayValueCRef = mayValue;
  gFunctionWasApplied = false;
  mayValueCRef.apply(&AccessValue);
  MOZ_RELEASE_ASSERT(gFunctionWasApplied);

  // Check that apply works with functors.
  IncrementTagFunctor tagIncrementer;
  MOZ_RELEASE_ASSERT(tagIncrementer.mBy.GetStatus() == eWasConstructed);
  mayValue = Some(BasicValue(1));
  mayValue.apply(tagIncrementer);
  MOZ_RELEASE_ASSERT(mayValue->GetTag() == 2);
  MOZ_RELEASE_ASSERT(tagIncrementer.mBy.GetStatus() == eWasConstructed);

  // Check that apply works with lambda expressions.
  int32_t two = 2;
  gFunctionWasApplied = false;
  mayValue = Some(BasicValue(2));
  mayValue.apply([&](BasicValue& aVal) { aVal.SetTag(aVal.GetTag() * two); });
  MOZ_RELEASE_ASSERT(mayValue->GetTag() == 4);
  mayValue.apply([=](BasicValue& aVal) { aVal.SetTag(aVal.GetTag() * two); });
  MOZ_RELEASE_ASSERT(mayValue->GetTag() == 8);
  mayValueCRef.apply([&](const BasicValue& aVal) { gFunctionWasApplied = true; });
  MOZ_RELEASE_ASSERT(gFunctionWasApplied == true);

  return true;
}

static bool
TestSomeNullptrConversion()
{
  Maybe<int*> m1 = Some(nullptr);
  MOZ_RELEASE_ASSERT(m1.isSome());
  MOZ_RELEASE_ASSERT(m1);
  MOZ_RELEASE_ASSERT(!*m1);

  auto m2 = ReturnSomeNullptr();
  MOZ_RELEASE_ASSERT(m2.isSome());
  MOZ_RELEASE_ASSERT(m2);
  MOZ_RELEASE_ASSERT(!*m2);

  Maybe<decltype(nullptr)> m3 = Some(nullptr);
  MOZ_RELEASE_ASSERT(m3.isSome());
  MOZ_RELEASE_ASSERT(m3);
  MOZ_RELEASE_ASSERT(*m3 == nullptr);

  D d(Some(nullptr));

  return true;
}

static bool
TestFunctionalAccessors()
{
  BasicValue value(9);
  sStaticBasicValue = new BasicValue(9);

  // Check that the 'some' case of functional accessors works.
  Maybe<BasicValue> someValue = Some(BasicValue(3));
  MOZ_RELEASE_ASSERT(someValue.valueOr(value) == BasicValue(3));
  static_assert(IsSame<BasicValue,
                       DECLTYPE(someValue.valueOr(value))>::value,
                "valueOr should return a BasicValue");
  MOZ_RELEASE_ASSERT(someValue.valueOrFrom(&MakeBasicValue) == BasicValue(3));
  static_assert(IsSame<BasicValue,
                       DECLTYPE(someValue.valueOrFrom(&MakeBasicValue))>::value,
                "valueOrFrom should return a BasicValue");
  MOZ_RELEASE_ASSERT(someValue.ptrOr(&value) != &value);
  static_assert(IsSame<BasicValue*,
                       DECLTYPE(someValue.ptrOr(&value))>::value,
                "ptrOr should return a BasicValue*");
  MOZ_RELEASE_ASSERT(*someValue.ptrOrFrom(&MakeBasicValuePtr) == BasicValue(3));
  static_assert(IsSame<BasicValue*,
                       DECLTYPE(someValue.ptrOrFrom(&MakeBasicValuePtr))>::value,
                "ptrOrFrom should return a BasicValue*");
  MOZ_RELEASE_ASSERT(someValue.refOr(value) == BasicValue(3));
  static_assert(IsSame<BasicValue&,
                       DECLTYPE(someValue.refOr(value))>::value,
                "refOr should return a BasicValue&");
  MOZ_RELEASE_ASSERT(someValue.refOrFrom(&MakeBasicValueRef) == BasicValue(3));
  static_assert(IsSame<BasicValue&,
                       DECLTYPE(someValue.refOrFrom(&MakeBasicValueRef))>::value,
                "refOrFrom should return a BasicValue&");

  // Check that the 'some' case works through a const reference.
  const Maybe<BasicValue>& someValueCRef = someValue;
  MOZ_RELEASE_ASSERT(someValueCRef.valueOr(value) == BasicValue(3));
  static_assert(IsSame<BasicValue,
                       DECLTYPE(someValueCRef.valueOr(value))>::value,
                "valueOr should return a BasicValue");
  MOZ_RELEASE_ASSERT(someValueCRef.valueOrFrom(&MakeBasicValue) == BasicValue(3));
  static_assert(IsSame<BasicValue,
                       DECLTYPE(someValueCRef.valueOrFrom(&MakeBasicValue))>::value,
                "valueOrFrom should return a BasicValue");
  MOZ_RELEASE_ASSERT(someValueCRef.ptrOr(&value) != &value);
  static_assert(IsSame<const BasicValue*,
                       DECLTYPE(someValueCRef.ptrOr(&value))>::value,
                "ptrOr should return a const BasicValue*");
  MOZ_RELEASE_ASSERT(*someValueCRef.ptrOrFrom(&MakeBasicValuePtr) == BasicValue(3));
  static_assert(IsSame<const BasicValue*,
                       DECLTYPE(someValueCRef.ptrOrFrom(&MakeBasicValuePtr))>::value,
                "ptrOrFrom should return a const BasicValue*");
  MOZ_RELEASE_ASSERT(someValueCRef.refOr(value) == BasicValue(3));
  static_assert(IsSame<const BasicValue&,
                       DECLTYPE(someValueCRef.refOr(value))>::value,
                "refOr should return a const BasicValue&");
  MOZ_RELEASE_ASSERT(someValueCRef.refOrFrom(&MakeBasicValueRef) == BasicValue(3));
  static_assert(IsSame<const BasicValue&,
                       DECLTYPE(someValueCRef.refOrFrom(&MakeBasicValueRef))>::value,
                "refOrFrom should return a const BasicValue&");

  // Check that the 'none' case of functional accessors works.
  Maybe<BasicValue> noneValue;
  MOZ_RELEASE_ASSERT(noneValue.valueOr(value) == BasicValue(9));
  static_assert(IsSame<BasicValue,
                       DECLTYPE(noneValue.valueOr(value))>::value,
                "valueOr should return a BasicValue");
  MOZ_RELEASE_ASSERT(noneValue.valueOrFrom(&MakeBasicValue) == BasicValue(9));
  static_assert(IsSame<BasicValue,
                       DECLTYPE(noneValue.valueOrFrom(&MakeBasicValue))>::value,
                "valueOrFrom should return a BasicValue");
  MOZ_RELEASE_ASSERT(noneValue.ptrOr(&value) == &value);
  static_assert(IsSame<BasicValue*,
                       DECLTYPE(noneValue.ptrOr(&value))>::value,
                "ptrOr should return a BasicValue*");
  MOZ_RELEASE_ASSERT(*noneValue.ptrOrFrom(&MakeBasicValuePtr) == BasicValue(9));
  static_assert(IsSame<BasicValue*,
                       DECLTYPE(noneValue.ptrOrFrom(&MakeBasicValuePtr))>::value,
                "ptrOrFrom should return a BasicValue*");
  MOZ_RELEASE_ASSERT(noneValue.refOr(value) == BasicValue(9));
  static_assert(IsSame<BasicValue&,
                       DECLTYPE(noneValue.refOr(value))>::value,
                "refOr should return a BasicValue&");
  MOZ_RELEASE_ASSERT(noneValue.refOrFrom(&MakeBasicValueRef) == BasicValue(9));
  static_assert(IsSame<BasicValue&,
                       DECLTYPE(noneValue.refOrFrom(&MakeBasicValueRef))>::value,
                "refOrFrom should return a BasicValue&");

  // Check that the 'none' case works through a const reference.
  const Maybe<BasicValue>& noneValueCRef = noneValue;
  MOZ_RELEASE_ASSERT(noneValueCRef.valueOr(value) == BasicValue(9));
  static_assert(IsSame<BasicValue,
                       DECLTYPE(noneValueCRef.valueOr(value))>::value,
                "valueOr should return a BasicValue");
  MOZ_RELEASE_ASSERT(noneValueCRef.valueOrFrom(&MakeBasicValue) == BasicValue(9));
  static_assert(IsSame<BasicValue,
                       DECLTYPE(noneValueCRef.valueOrFrom(&MakeBasicValue))>::value,
                "valueOrFrom should return a BasicValue");
  MOZ_RELEASE_ASSERT(noneValueCRef.ptrOr(&value) == &value);
  static_assert(IsSame<const BasicValue*,
                       DECLTYPE(noneValueCRef.ptrOr(&value))>::value,
//.........这里部分代码省略.........

static bool
TestBasicFeatures()
{
  // Check that a Maybe<T> is initialized to Nothing.
  Maybe<BasicValue> mayValue;
  static_assert(IsSame<BasicValue, DECLTYPE(mayValue)::ValueType>::value,
                "Should have BasicValue ValueType");
  MOZ_RELEASE_ASSERT(!mayValue);
  MOZ_RELEASE_ASSERT(!mayValue.isSome());
  MOZ_RELEASE_ASSERT(mayValue.isNothing());

  // Check that emplace() default constructs and the accessors work.
  mayValue.emplace();
  MOZ_RELEASE_ASSERT(mayValue);
  MOZ_RELEASE_ASSERT(mayValue.isSome());
  MOZ_RELEASE_ASSERT(!mayValue.isNothing());
  MOZ_RELEASE_ASSERT(*mayValue == BasicValue());
  MOZ_RELEASE_ASSERT(mayValue.value() == BasicValue());
  static_assert(IsSame<BasicValue, DECLTYPE(mayValue.value())>::value,
                "value() should return a BasicValue");
  MOZ_RELEASE_ASSERT(mayValue.ref() == BasicValue());
  static_assert(IsSame<BasicValue&, DECLTYPE(mayValue.ref())>::value,
                "ref() should return a BasicValue&");
  MOZ_RELEASE_ASSERT(mayValue.ptr() != nullptr);
  static_assert(IsSame<BasicValue*, DECLTYPE(mayValue.ptr())>::value,
                "ptr() should return a BasicValue*");
  MOZ_RELEASE_ASSERT(mayValue->GetStatus() == eWasDefaultConstructed);

  // Check that reset() works.
  mayValue.reset();
  MOZ_RELEASE_ASSERT(!mayValue);
  MOZ_RELEASE_ASSERT(!mayValue.isSome());
  MOZ_RELEASE_ASSERT(mayValue.isNothing());

  // Check that emplace(T1) calls the correct constructor.
  mayValue.emplace(1);
  MOZ_RELEASE_ASSERT(mayValue);
  MOZ_RELEASE_ASSERT(mayValue->GetStatus() == eWasConstructed);
  MOZ_RELEASE_ASSERT(mayValue->GetTag() == 1);
  mayValue.reset();
  MOZ_RELEASE_ASSERT(!mayValue);

  // Check that Some() and Nothing() work.
  mayValue = Some(BasicValue(2));
  MOZ_RELEASE_ASSERT(mayValue);
  MOZ_RELEASE_ASSERT(mayValue->GetStatus() == eWasMoveConstructed);
  MOZ_RELEASE_ASSERT(mayValue->GetTag() == 2);
  mayValue = Nothing();
  MOZ_RELEASE_ASSERT(!mayValue);

  // Check that the accessors work through a const ref.
  mayValue.emplace();
  const Maybe<BasicValue>& mayValueCRef = mayValue;
  MOZ_RELEASE_ASSERT(mayValueCRef);
  MOZ_RELEASE_ASSERT(mayValueCRef.isSome());
  MOZ_RELEASE_ASSERT(!mayValueCRef.isNothing());
  MOZ_RELEASE_ASSERT(*mayValueCRef == BasicValue());
  MOZ_RELEASE_ASSERT(mayValueCRef.value() == BasicValue());
  static_assert(IsSame<BasicValue, DECLTYPE(mayValueCRef.value())>::value,
                "value() should return a BasicValue");
  MOZ_RELEASE_ASSERT(mayValueCRef.ref() == BasicValue());
  static_assert(IsSame<const BasicValue&,
                       DECLTYPE(mayValueCRef.ref())>::value,
                "ref() should return a const BasicValue&");
  MOZ_RELEASE_ASSERT(mayValueCRef.ptr() != nullptr);
  static_assert(IsSame<const BasicValue*,
                       DECLTYPE(mayValueCRef.ptr())>::value,
                "ptr() should return a const BasicValue*");
  MOZ_RELEASE_ASSERT(mayValueCRef->GetStatus() == eWasDefaultConstructed);
  mayValue.reset();

  return true;
}

Maybe<uint64_t>
nsStringInputStream::ExpectedSerializedLength()
{
  return Some(static_cast<uint64_t>(Length()));
}

static Maybe<Base*>
ReturnDerivedPointer()
{
  Derived* d = nullptr;
  return Some(d);
}

void ProfileBuffer::StreamSamplesToJSON(SpliceableJSONWriter& aWriter, int aThreadId,
                                        float aSinceTime, JSRuntime* aRuntime,
                                        UniqueStacks& aUniqueStacks)
{
  Maybe<ProfileSample> sample;
  int readPos = mReadPos;
  int currentThreadID = -1;
  Maybe<float> currentTime;
  UniquePtr<char[]> tagBuff = MakeUnique<char[]>(DYNAMIC_MAX_STRING);

  while (readPos != mWritePos) {
    ProfileEntry entry = mEntries[readPos];
    if (entry.mTagName == 'T') {
      currentThreadID = entry.mTagInt;
      currentTime.reset();
      int readAheadPos = (readPos + 1) % mEntrySize;
      if (readAheadPos != mWritePos) {
        ProfileEntry readAheadEntry = mEntries[readAheadPos];
        if (readAheadEntry.mTagName == 't') {
          currentTime = Some(readAheadEntry.mTagFloat);
        }
      }
    }
    if (currentThreadID == aThreadId && (currentTime.isNothing() || *currentTime >= aSinceTime)) {
      switch (entry.mTagName) {
      case 'r':
        if (sample.isSome()) {
          sample->mResponsiveness = Some(entry.mTagFloat);
        }
        break;
      case 'p':
        if (sample.isSome()) {
          sample->mPower = Some(entry.mTagFloat);
        }
        break;
      case 'R':
        if (sample.isSome()) {
          sample->mRSS = Some(entry.mTagFloat);
        }
        break;
      case 'U':
        if (sample.isSome()) {
          sample->mUSS = Some(entry.mTagFloat);
         }
        break;
      case 'f':
        if (sample.isSome()) {
          sample->mFrameNumber = Some(entry.mTagInt);
        }
        break;
      case 's':
        {
          // end the previous sample if there was one
          if (sample.isSome()) {
            WriteSample(aWriter, *sample);
            sample.reset();
          }
          // begin the next sample
          sample.emplace();
          sample->mTime = currentTime;

          // Seek forward through the entire sample, looking for frames
          // this is an easier approach to reason about than adding more
          // control variables and cases to the loop that goes through the buffer once

          UniqueStacks::Stack stack =
            aUniqueStacks.BeginStack(UniqueStacks::OnStackFrameKey("(root)"));

          int framePos = (readPos + 1) % mEntrySize;
          ProfileEntry frame = mEntries[framePos];
          while (framePos != mWritePos && frame.mTagName != 's' && frame.mTagName != 'T') {
            int incBy = 1;
            frame = mEntries[framePos];

            // Read ahead to the next tag, if it's a 'd' tag process it now
            const char* tagStringData = frame.mTagData;
            int readAheadPos = (framePos + 1) % mEntrySize;
            // Make sure the string is always null terminated if it fills up
            // DYNAMIC_MAX_STRING-2
            tagBuff[DYNAMIC_MAX_STRING-1] = '\0';

            if (readAheadPos != mWritePos && mEntries[readAheadPos].mTagName == 'd') {
              tagStringData = processDynamicTag(framePos, &incBy, tagBuff.get());
            }

            // Write one frame. It can have either
            // 1. only location - 'l' containing a memory address
            // 2. location and line number - 'c' followed by 'd's,
            // an optional 'n' and an optional 'y'
            // 3. a JIT return address - 'j' containing native code address
            if (frame.mTagName == 'l') {
              // Bug 753041
              // We need a double cast here to tell GCC that we don't want to sign
              // extend 32-bit addresses starting with 0xFXXXXXX.
              unsigned long long pc = (unsigned long long)(uintptr_t)frame.mTagPtr;
              snprintf(tagBuff.get(), DYNAMIC_MAX_STRING, "%#llx", pc);
              stack.AppendFrame(UniqueStacks::OnStackFrameKey(tagBuff.get()));
            } else if (frame.mTagName == 'c') {
              UniqueStacks::OnStackFrameKey frameKey(tagStringData);
              readAheadPos = (framePos + incBy) % mEntrySize;
//.........这里部分代码省略.........