IDL: make optional arguments (without default) explicit sometimes

Source/bindings/core/v8/Optional.h

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef Optional_h
+#define Optional_h
+
+#include "bindings/core/v8/Dictionary.h"
+#include "bindings/core/v8/ScriptValue.h"
+#include "bindings/core/v8/V8StringResource.h"
+#include "wtf/Assertions.h"
+
+namespace blink {
+
+template <typename T>
+inline T defaultValue()
+{
+    return T();
+}
+
+template <>
+inline float defaultValue()
+{
+    return std::numeric_limits<float>::quiet_NaN();
+}
+
+template <>
+inline double defaultValue()
+{
+    return std::numeric_limits<double>::quiet_NaN();
+}
+
+template <typename T>
+class Optional {
+public:
+    template <typename U>
+    explicit Optional(const U& value, bool isMissing = false)
+        : m_value(value)
+        , m_isMissing(isMissing) { }
+
+    Optional(const Optional& other)
+        : m_value(other.m_value)
+        , m_isMissing(other.m_isMissing) { }
+
+    template <typename U>
+    Optional(const Optional<U>& other)
+        : m_value(other.get())
+        , m_isMissing(other.isMissing()) { }
+
+    T get() const { return m_isMissing ? defaultValue<T>() : m_value; }
+    bool isMissing() const { return m_isMissing; }
+
+    operator T() const
+    {
+        return get();
+    }
+
+private:
+    T m_value;
+    bool m_isMissing;
+};
+
+// Partial specialization that adds conversion from T* to PassRefPtr<T>.
+template <typename T>
+class Optional<T*> {
+public:
+    template <typename U>
+    explicit Optional(U* value, bool isMissing = false)
+        : m_value(value)
+        , m_isMissing(isMissing)
+    {
+    }
+
+    T* get() const { return m_isMissing ? nullptr : m_value; }
+    bool isMissing() const { return m_isMissing; }
+
+    operator T*() const
+    {
+        return get();
+    }
+    operator PassRefPtr<T>() const
+    {
+        return PassRefPtr<T>(get());
+    }
+
+private:
+    T* m_value;
+    bool m_isMissing;
+};
+
+// Partial specialization that adds conversion from RefPtr<T> to PassRefPtr<T> and T*.
+template <typename T>
+class Optional<RefPtr<T> > {
+public:
+    explicit Optional(T* value, bool isMissing = false)
+        : m_value(value)
+        , m_isMissing(isMissing)
+    {
+    }
+
+    template <typename U>
+    explicit Optional(const RefPtr<U>& value, bool isMissing = false)
+        : m_value(value)
+        , m_isMissing(isMissing)
+    {
+    }
+
+    PassRefPtr<T> get() const { return m_isMissing ? nullptr : m_value; }
+    bool isMissing() const { return m_isMissing; }
+
+    operator PassRefPtr<T>() const
+    {
+        return get();
+    }
+    operator T*() const
+    {
+        return m_isMissing ? nullptr : m_value.get();
+    }
+
+private:
+    RefPtr<T> m_value;
+    bool m_isMissing;
+};
+
+// Partial specialization that adds conversion from OwnPtr<T> to PassOwnPtr<T>.
+// FIXME: This specialization is odd in that it actually holds on to a non-const
+// reference to the original value, and mutates it. It would be great to avoid
+// that, e.g. by not passing OwnPtr<> argument from the bindings layer.
+template <typename T>
+class Optional<OwnPtr<T> > {
+public:
+    explicit Optional(OwnPtr<T>& value, bool isMissing = false)
+        : m_value(value)
+        , m_isMissing(isMissing)
+    {
+    }
+
+    PassOwnPtr<T> get() { return m_isMissing ? PassOwnPtr<T>() : m_value.release(); }
+    bool isMissing() const { return m_isMissing; }
+
+    operator PassOwnPtr<T>()
+    {
+        return get();
+    }
+
+private:
+    OwnPtr<T>& m_value;
+    bool m_isMissing;
+};
+
+// Partial specialization that adds conversion from Member<T> to T*.
+template <typename T>
+class Optional<Member<T> > {
+    STACK_ALLOCATED();
+public:
+    explicit Optional(T* value, bool isMissing = false)
+        : m_value(value)
+        , m_isMissing(isMissing)
+    {
+    }
+
+    T* get() { return m_isMissing ? nullptr : m_value.get(); }
+    bool isMissing() const { return m_isMissing; }
+
+    operator T*()
+    {
+        return get();
+    }
+
+private:
+    Member<T> m_value;
+    bool m_isMissing;
+};
+
+// Partial specialization that adds conversion from V8StringResource<Mode> to String and AtomicString.
+template <V8StringResourceMode Mode>
+class Optional<V8StringResource<Mode> > {
+public:
+    explicit Optional(const V8StringResource<Mode>& value, bool isMissing = false)
+        : m_value(value)
+        , m_isMissing(isMissing)
+    {
+    }
+
+    String get() const { return m_isMissing ? String() : m_value; }
+    bool isMissing() const { return m_isMissing; }
+
+    operator String() const
+    {
+        return get();
+    }
+    operator AtomicString() const
+    {
+        return m_isMissing ? AtomicString() : m_value;
+    }
+
+private:
+    const V8StringResource<Mode>& m_value;
+    bool m_isMissing;
+};
+
+template <typename T>
+Optional<T> makeOptionalMissing()
+{
+    return Optional<T>(defaultValue<T>(), true);
+}
+
+template <typename T>
+Optional<T> makeOptional(T value, bool isMissing = false)
+{
+    return Optional<T>(value, isMissing);
+}
+
+template <typename T>
+Optional<RefPtr<T> > makeOptional(const RefPtr<T>& value, bool isMissing = false)
+{
+    return Optional<RefPtr<T> >(value, isMissing);
+}
+
+template <typename T>
+Optional<OwnPtr<T> > makeOptional(OwnPtr<T>& value, bool isMissing = false)
+{
+    return Optional<OwnPtr<T> >(value, isMissing);
+}
+
+} // namespace blink
+
+#endif // Optional_h