IDL: make optional arguments (without default) explicit sometimes

Source/bindings/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 "wtf/Assertions.h"
+
+namespace WebCore {
+
+template <typename T>
+class Optional {
+public:
+    Optional(const T& value, bool isMissing)
+        : 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)

[Jens Widell, 2014/06/17 09:53:37]

This operator might be useful (or not work at all) when dealing with for
instance string arguments. In the generated code, they will be of type
V8StringResource<>. In the C++ implementation, they argument will typically be
either WTF::String or WTF::AtomicString to which V8StringResource<> can be
converted.

So the idea would be that the generated code calls the function with
Optional<V8StringResource<> >,  and the C++ implementation is declared to take
either Optional<String> or Optional<AtomicString>, and automatic type conversion
takes care of the rest.  I don't know that this works, since I haven't tested
it.

+        : m_value(other.m_value)
+        , m_isMissing(other.m_isMissing) { }
+
+    Optional& operator=(const Optional& other)
+    {
+        m_value = other.m_value;
+        m_isMissing = other.m_isMissing;
+        return *this;
+    }
+
+    T get() const { ASSERT(!m_isMissing); return m_value; }
+    bool isMissing() const { return m_isMissing; }
+
+    operator bool() const { return !m_isMissing && m_value; }
+
+    bool operator==(const Optional& other) const
+    {
+        return (m_isMissing && other.m_isMissing) || (!m_isMissing && !other.m_isMissing && m_value == other.m_value);
+    }
+
+private:
+    T m_value;
+    bool m_isMissing;
+};
+
+template <typename T>
+Optional<T> makeOptional(T value, bool isMissing)
+{
+    return Optional<T>(value, isMissing);
+}
+
+} // namespace WebCore
+
+#endif // Optional_h