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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
#ifndef js_GCVariant_h
#define js_GCVariant_h
#include "mozilla/Variant.h"
#include "js/GCPolicyAPI.h"
#include "js/RootingAPI.h"
#include "js/TracingAPI.h"
namespace JS {
// These template specializations allow Variant to be used inside GC wrappers.
//
// When matching on GC wrappers around Variants, matching should be done on
// the wrapper itself. The matcher class's methods should take Handles or
// MutableHandles. For example,
//
// struct MyMatcher
// {
// using ReturnType = const char*;
// ReturnType match(HandleObject o) { return "object"; }
// ReturnType match(HandleScript s) { return "script"; }
// };
//
// Rooted<Variant<JSObject*, JSScript*>> v(cx, someScript);
// MyMatcher mm;
// v.match(mm);
//
// If you get compile errors about inability to upcast subclasses (e.g., from
// NativeObject* to JSObject*) and are inside js/src, be sure to also include
// "gc/Policy.h".
namespace detail {
template <typename... Ts>
struct GCVariantImplementation;
// The base case.
template <typename T>
struct GCVariantImplementation<T>
{
template <typename ConcreteVariant>
static void trace(JSTracer* trc, ConcreteVariant* v, const char* name) {
T& thing = v->template as<T>();
if (!mozilla::IsPointer<T>::value || thing)
GCPolicy<T>::trace(trc, &thing, name);
}
template <typename Matcher, typename ConcreteVariant>
static typename Matcher::ReturnType
match(Matcher& matcher, Handle<ConcreteVariant> v) {
const T& thing = v.get().template as<T>();
return matcher.match(Handle<T>::fromMarkedLocation(&thing));
}
template <typename Matcher, typename ConcreteVariant>
static typename Matcher::ReturnType
match(Matcher& matcher, MutableHandle<ConcreteVariant> v) {
T& thing = v.get().template as<T>();
return matcher.match(MutableHandle<T>::fromMarkedLocation(&thing));
}
};
// The inductive case.
template <typename T, typename... Ts>
struct GCVariantImplementation<T, Ts...>
{
using Next = GCVariantImplementation<Ts...>;
template <typename ConcreteVariant>
static void trace(JSTracer* trc, ConcreteVariant* v, const char* name) {
if (v->template is<T>()) {
T& thing = v->template as<T>();
if (!mozilla::IsPointer<T>::value || thing)
GCPolicy<T>::trace(trc, &thing, name);
} else {
Next::trace(trc, v, name);
}
}
template <typename Matcher, typename ConcreteVariant>
static typename Matcher::ReturnType
match(Matcher& matcher, Handle<ConcreteVariant> v) {
if (v.get().template is<T>()) {
const T& thing = v.get().template as<T>();
return matcher.match(Handle<T>::fromMarkedLocation(&thing));
}
return Next::match(matcher, v);
}
template <typename Matcher, typename ConcreteVariant>
static typename Matcher::ReturnType
match(Matcher& matcher, MutableHandle<ConcreteVariant> v) {
if (v.get().template is<T>()) {
T& thing = v.get().template as<T>();
return matcher.match(MutableHandle<T>::fromMarkedLocation(&thing));
}
return Next::match(matcher, v);
}
};
} // namespace detail
template <typename... Ts>
struct GCPolicy<mozilla::Variant<Ts...>>
{
using Impl = detail::GCVariantImplementation<Ts...>;
// Variants do not provide initial(). They do not have a default initial
// value and one must be provided.
static void trace(JSTracer* trc, mozilla::Variant<Ts...>* v, const char* name) {
Impl::trace(trc, v, name);
}
};
} // namespace JS
namespace js {
template <typename Wrapper, typename... Ts>
class WrappedPtrOperations<mozilla::Variant<Ts...>, Wrapper>
{
using Impl = JS::detail::GCVariantImplementation<Ts...>;
using Variant = mozilla::Variant<Ts...>;
const Variant& variant() const { return static_cast<const Wrapper*>(this)->get(); }
public:
template <typename T>
bool is() const {
return variant().template is<T>();
}
template <typename T>
JS::Handle<T> as() const {
return Handle<T>::fromMarkedLocation(&variant().template as<T>());
}
template <typename Matcher>
typename Matcher::ReturnType
match(Matcher& matcher) const {
return Impl::match(matcher, JS::Handle<Variant>::fromMarkedLocation(&variant()));
}
};
template <typename Wrapper, typename... Ts>
class MutableWrappedPtrOperations<mozilla::Variant<Ts...>, Wrapper>
: public WrappedPtrOperations<mozilla::Variant<Ts...>, Wrapper>
{
using Impl = JS::detail::GCVariantImplementation<Ts...>;
using Variant = mozilla::Variant<Ts...>;
const Variant& variant() const { return static_cast<const Wrapper*>(this)->get(); }
Variant& variant() { return static_cast<Wrapper*>(this)->get(); }
public:
template <typename T>
JS::MutableHandle<T> as() {
return JS::MutableHandle<T>::fromMarkedLocation(&variant().template as<T>());
}
template <typename Matcher>
typename Matcher::ReturnType
match(Matcher& matcher) {
return Impl::match(matcher, JS::MutableHandle<Variant>::fromMarkedLocation(&variant()));
}
};
} // namespace js
#endif // js_GCVariant_h
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