1 files changed, 91 insertions, 0 deletions
diff --git a/js/src/vm/List.h b/js/src/vm/List.h
new file mode 100644
index 0000000000..96106b65d7
--- /dev/null
+++ b/js/src/vm/List.h
@@ -0,0 +1,91 @@
+/* -*- 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/. */
+
+#ifndef vm_List_h
+#define vm_List_h
+
+#include "NamespaceImports.h"
+#include "js/Value.h"
+#include "vm/NativeObject.h"
+
+namespace js {
+
+/**
+ * The List specification type, ECMA-262 6.2.1.
+ * <https://tc39.github.io/ecma262/#sec-list-and-record-specification-type>
+ *
+ * Lists are simple mutable sequences of values. Many standards use them.
+ * Abstractly, they're not objects; they don't have properties or prototypes;
+ * they're for internal specification use only. ListObject is our most direct
+ * implementation of a List: store the values in the slots of a JSObject.
+ *
+ * We often implement Lists in other ways. For example, builtin/Utilities.js
+ * contains a completely unrelated List constructor that's used in self-hosted
+ * code. And AsyncGeneratorObject optimizes away the ListObject in the common
+ * case where its internal queue never holds more than one element.
+ *
+ * ListObjects must not be exposed to content scripts.
+ */
+class ListObject : public NativeObject {
+ public:
+  static const JSClass class_;
+
+  [[nodiscard]] inline static ListObject* create(JSContext* cx);
+
+  uint32_t length() const { return getDenseInitializedLength(); }
+
+  bool isEmpty() const { return length() == 0; }
+
+  const Value& get(uint32_t index) const { return getDenseElement(index); }
+
+  template <class T>
+  T& getAs(uint32_t index) const {
+    return get(index).toObject().as<T>();
+  }
+
+  /**
+   * Add an element to the end of the list. Returns false on OOM.
+   */
+  [[nodiscard]] inline bool append(JSContext* cx, HandleValue value);
+
+  /**
+   * Adds |value| and |size| elements to a list consisting of (value, size)
+   * pairs stored in successive elements.
+   *
+   * This function is intended for use by streams code's queue-with-sizes data
+   * structure and related operations.  See builtin/streams/QueueWithSizes*.
+   * (You *could* use this on any list of even length without issue, but it's
+   * hard to imagine realistic situations where you'd want to...)
+   */
+  [[nodiscard]] inline bool appendValueAndSize(JSContext* cx, HandleValue value,
+                                               double size);
+
+  /**
+   * Remove and return the first element of the list.
+   *
+   * Precondition: This list is not empty.
+   */
+  inline JS::Value popFirst(JSContext* cx);
+
+  /**
+   * Remove the first two elements from a nonempty list of (value, size) pairs
+   * of elements.
+   */
+  inline void popFirstPair(JSContext* cx);
+
+  /**
+   * Remove and return the first element of the list.
+   *
+   * Precondition: This list is not empty, and the first element
+   * is an object of class T.
+   */
+  template <class T>
+  inline T& popFirstAs(JSContext* cx);
+};
+
+}  // namespace js
+
+#endif  // vm_List_h