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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
* vim: set ts=8 sts=4 et sw=4 tw=99:
* 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 */
/* JS::PropertyKey implementation. */
#ifndef js_PropertyKey_h
#define js_PropertyKey_h
#include "mozilla/Attributes.h"
#include "js/Value.h"
struct JSContext;
namespace JS {
class PropertyKey;
namespace detail {
extern JS_PUBLIC_API(bool)
ToPropertyKeySlow(JSContext *cx, HandleValue v, PropertyKey *key);
} // namespace detail
* A PropertyKey is a key used to access some property on an object. It is a
* natural way to represent a property accessed using a JavaScript value.
* PropertyKey can represent indexes, named properties, and ES6 symbols. The
* latter aren't implemented in SpiderMonkey yet, but PropertyKey carves out
* space for them.
class PropertyKey
Value v;
friend JS_PUBLIC_API(bool) detail::ToPropertyKeySlow(JSContext *cx, HandleValue v, PropertyKey *key);
explicit PropertyKey(uint32_t index) : v(PrivateUint32Value(index)) {}
* An index is a string property name whose characters exactly spell out an
* unsigned 32-bit integer in decimal: "0", "1", "2", ...., "4294967294",
* "4294967295".
bool isIndex(uint32_t *index) {
// The implementation here assumes that private uint32_t are stored
// using the int32_t representation. This is purely an implementation
// detail: embedders must not rely upon this!
if (!v.isInt32())
return false;
*index = v.toPrivateUint32();
return true;
* A name is a string property name which is *not* an index. Note that by
* the ECMAScript language grammar, any dotted property access |obj.prop|
* will access a named property.
bool isName(JSString **str) {
uint32_t dummy;
if (isIndex(&dummy))
return false;
*str = v.toString();
return true;
* A symbol is a property name that's a Symbol, a particular kind of object
* in ES6. It is the only kind of property name that's not a string.
* SpiderMonkey doesn't yet implement symbols, but we're carving out API
* space for them in advance.
bool isSymbol() {
return false;
inline bool
ToPropertyKey(JSContext *cx, HandleValue v, PropertyKey *key)
if (v.isInt32() && v.toInt32() >= 0) {
*key = PropertyKey(uint32_t(v.toInt32()));
return true;
return detail::ToPropertyKeySlow(cx, v, key);
} // namespace JS
#endif /* js_PropertyKey_h */