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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
* vim: set ts=8 sts=2 et sw=2 tw=80:
* 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/. */
/*
* A convenience class that makes it easy to perform the operations of a for-of
* loop.
*/
#ifndef js_ForOfIterator_h
#define js_ForOfIterator_h
#include "mozilla/Attributes.h" // MOZ_STACK_CLASS
#include <stdint.h> // UINT32_MAX, uint32_t
#include "jstypes.h" // JS_PUBLIC_API
#include "js/RootingAPI.h" // JS::{Handle,Rooted}
#include "js/Value.h" // JS::Value, JS::{,Mutable}Handle<JS::Value>
struct JS_PUBLIC_API JSContext;
class JS_PUBLIC_API JSObject;
namespace JS {
/**
* A convenience class for imitating a JS for-of loop. Typical usage:
*
* JS::ForOfIterator it(cx);
* if (!it.init(iterable)) {
* return false;
* }
* JS::Rooted<JS::Value> val(cx);
* while (true) {
* bool done;
* if (!it.next(&val, &done)) {
* return false;
* }
* if (done) {
* break;
* }
* if (!DoStuff(cx, val)) {
* return false;
* }
* }
*/
class MOZ_STACK_CLASS JS_PUBLIC_API ForOfIterator {
protected:
JSContext* cx_;
// Use realm fuses (see `IsArrayWithDefaultIterator` in vm/Iteration.cpp) to
// try to optimize iteration across arrays.
//
// Case 1: Regular Iteration
// iterator - pointer to the iterator object.
// nextMethod - value of |iterator|.next.
// index - fixed to NOT_ARRAY (== UINT32_MAX)
//
// Case 2: Optimized Array Iteration
// iterator - pointer to the array object.
// nextMethod - the undefined value.
// index - current position in array.
//
// The cases are distinguished by whether |index == NOT_ARRAY|.
Rooted<JSObject*> iterator;
Rooted<Value> nextMethod;
static constexpr uint32_t NOT_ARRAY = UINT32_MAX;
uint32_t index = NOT_ARRAY;
ForOfIterator(const ForOfIterator&) = delete;
ForOfIterator& operator=(const ForOfIterator&) = delete;
public:
explicit ForOfIterator(JSContext* cx)
: cx_(cx), iterator(cx), nextMethod(cx) {}
enum NonIterableBehavior { ThrowOnNonIterable, AllowNonIterable };
/**
* Initialize the iterator. If AllowNonIterable is passed then if getting
* the @@iterator property from iterable returns undefined init() will just
* return true instead of throwing. Callers must then check
* valueIsIterable() before continuing with the iteration.
*/
[[nodiscard]] bool init(
Handle<Value> iterable,
NonIterableBehavior nonIterableBehavior = ThrowOnNonIterable);
/**
* Get the next value from the iterator. If false *done is true
* after this call, do not examine val.
*/
[[nodiscard]] bool next(MutableHandle<Value> val, bool* done);
/**
* Close the iterator.
* For the case that completion type is throw.
*/
void closeThrow();
/**
* If initialized with throwOnNonCallable = false, check whether
* the value is iterable.
*/
bool valueIsIterable() const { return iterator; }
private:
inline bool nextFromOptimizedArray(MutableHandle<Value> val, bool* done);
};
} // namespace JS
#endif // js_ForOfIterator_h
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