1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
2  * vim: set ts=8 sts=2 et sw=2 tw=80:
3  * This Source Code Form is subject to the terms of the Mozilla Public
4  * License, v. 2.0. If a copy of the MPL was not distributed with this
5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
6 
7 #ifndef vm_List_h
8 #define vm_List_h
9 
10 #include "NamespaceImports.h"
11 #include "js/Value.h"
12 #include "vm/NativeObject.h"
13 
14 namespace js {
15 
16 /**
17  * The List specification type, ECMA-262 6.2.1.
18  * <https://tc39.github.io/ecma262/#sec-list-and-record-specification-type>
19  *
20  * Lists are simple mutable sequences of values. Many standards use them.
21  * Abstractly, they're not objects; they don't have properties or prototypes;
22  * they're for internal specification use only. ListObject is our most direct
23  * implementation of a List: store the values in the slots of a JSObject.
24  *
25  * We often implement Lists in other ways. For example, builtin/Utilities.js
26  * contains a completely unrelated List constructor that's used in self-hosted
27  * code. And AsyncGeneratorObject optimizes away the ListObject in the common
28  * case where its internal queue never holds more than one element.
29  *
30  * ListObjects must not be exposed to content scripts.
31  */
32 class ListObject : public NativeObject {
33  public:
34   static const JSClass class_;
35 
36   [[nodiscard]] inline static ListObject* create(JSContext* cx);
37 
length()38   uint32_t length() const { return getDenseInitializedLength(); }
39 
isEmpty()40   bool isEmpty() const { return length() == 0; }
41 
get(uint32_t index)42   const Value& get(uint32_t index) const { return getDenseElement(index); }
43 
44   template <class T>
getAs(uint32_t index)45   T& getAs(uint32_t index) const {
46     return get(index).toObject().as<T>();
47   }
48 
49   /**
50    * Add an element to the end of the list. Returns false on OOM.
51    */
52   [[nodiscard]] inline bool append(JSContext* cx, HandleValue value);
53 
54   /**
55    * Adds |value| and |size| elements to a list consisting of (value, size)
56    * pairs stored in successive elements.
57    *
58    * This function is intended for use by streams code's queue-with-sizes data
59    * structure and related operations.  See builtin/streams/QueueWithSizes*.
60    * (You *could* use this on any list of even length without issue, but it's
61    * hard to imagine realistic situations where you'd want to...)
62    */
63   [[nodiscard]] inline bool appendValueAndSize(JSContext* cx, HandleValue value,
64                                                double size);
65 
66   /**
67    * Remove and return the first element of the list.
68    *
69    * Precondition: This list is not empty.
70    */
71   inline JS::Value popFirst(JSContext* cx);
72 
73   /**
74    * Remove the first two elements from a nonempty list of (value, size) pairs
75    * of elements.
76    */
77   inline void popFirstPair(JSContext* cx);
78 
79   /**
80    * Remove and return the first element of the list.
81    *
82    * Precondition: This list is not empty, and the first element
83    * is an object of class T.
84    */
85   template <class T>
86   inline T& popFirstAs(JSContext* cx);
87 };
88 
89 }  // namespace js
90 
91 #endif  // vm_List_h
92