gecko-dev/toolkit/modules/Dict.jsm

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JavaScript

/* 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/. */
"use strict";
this.EXPORTED_SYMBOLS = ["Dict"];
/**
* Transforms a given key into a property name guaranteed not to collide with
* any built-ins.
*/
function convert(aKey) {
return ":" + aKey;
}
/**
* Transforms a property into a key suitable for providing to the outside world.
*/
function unconvert(aProp) {
return aProp.substr(1);
}
/**
* A dictionary of strings to arbitrary JS objects. This should be used whenever
* the keys are potentially arbitrary, to avoid collisions with built-in
* properties.
*
* @param aInitial An object containing the initial keys and values of this
* dictionary. Only the "own" enumerable properties of the
* object are considered.
* If |aInitial| is a string, it is assumed to be JSON and parsed into an object.
*/
this.Dict = function Dict(aInitial) {
if (aInitial === undefined)
aInitial = {};
if (typeof aInitial == "string")
aInitial = JSON.parse(aInitial);
var items = {}, count = 0;
// That we don't look up the prototype chain is guaranteed by Iterator.
for (var [key, val] in Iterator(aInitial)) {
items[convert(key)] = val;
count++;
}
this._state = {count: count, items: items};
return Object.freeze(this);
}
Dict.prototype = Object.freeze({
/**
* The number of items in the dictionary.
*/
get count() {
return this._state.count;
},
/**
* Gets the value for a key from the dictionary. If the key is not a string,
* it will be converted to a string before the lookup happens.
*
* @param aKey The key to look up
* @param [aDefault] An optional default value to return if the key is not
* present. Defaults to |undefined|.
* @returns The item, or aDefault if it isn't found.
*/
get: function Dict_get(aKey, aDefault) {
var prop = convert(aKey);
var items = this._state.items;
return items.hasOwnProperty(prop) ? items[prop] : aDefault;
},
/**
* Sets the value for a key in the dictionary. If the key is a not a string,
* it will be converted to a string before the set happens.
*/
set: function Dict_set(aKey, aValue) {
var prop = convert(aKey);
var items = this._state.items;
if (!items.hasOwnProperty(prop))
this._state.count++;
items[prop] = aValue;
},
/**
* Sets a lazy getter function for a key's value. If the key is a not a string,
* it will be converted to a string before the set happens.
* @param aKey
* The key to set
* @param aThunk
* A getter function to be called the first time the value for aKey is
* retrieved. It is guaranteed that aThunk wouldn't be called more
* than once. Note that the key value may be retrieved either
* directly, by |get|, or indirectly, by |listvalues| or by iterating
* |values|. For the later, the value is only retrieved if and when
* the iterator gets to the value in question. Also note that calling
* |has| for a lazy-key does not invoke aThunk.
*
* @note No context is provided for aThunk when it's invoked.
* Use Function.bind if you wish to run it in a certain context.
*/
setAsLazyGetter: function Dict_setAsLazyGetter(aKey, aThunk) {
let prop = convert(aKey);
let items = this._state.items;
if (!items.hasOwnProperty(prop))
this._state.count++;
Object.defineProperty(items, prop, {
get: function() {
delete items[prop];
return items[prop] = aThunk();
},
configurable: true,
enumerable: true
});
},
/**
* Returns whether a key is set as a lazy getter. This returns
* true only if the getter function was not called already.
* @param aKey
* The key to look up.
* @returns whether aKey is set as a lazy getter.
*/
isLazyGetter: function Dict_isLazyGetter(aKey) {
let descriptor = Object.getOwnPropertyDescriptor(this._state.items,
convert(aKey));
return (descriptor && descriptor.get != null);
},
/**
* Returns whether a key is in the dictionary. If the key is a not a string,
* it will be converted to a string before the lookup happens.
*/
has: function Dict_has(aKey) {
return (this._state.items.hasOwnProperty(convert(aKey)));
},
/**
* Deletes a key from the dictionary. If the key is a not a string, it will be
* converted to a string before the delete happens.
*
* @returns true if the key was found, false if it wasn't.
*/
del: function Dict_del(aKey) {
var prop = convert(aKey);
if (this._state.items.hasOwnProperty(prop)) {
delete this._state.items[prop];
this._state.count--;
return true;
}
return false;
},
/**
* Returns a shallow copy of this dictionary.
*/
copy: function Dict_copy() {
var newItems = {};
for (var [key, val] in this.items)
newItems[key] = val;
return new Dict(newItems);
},
/*
* List and iterator functions
*
* No guarantees whatsoever are made about the order of elements.
*/
/**
* Returns a list of all the keys in the dictionary in an arbitrary order.
*/
listkeys: function Dict_listkeys() {
return [unconvert(k) for (k in this._state.items)];
},
/**
* Returns a list of all the values in the dictionary in an arbitrary order.
*/
listvalues: function Dict_listvalues() {
var items = this._state.items;
return [items[k] for (k in items)];
},
/**
* Returns a list of all the items in the dictionary as key-value pairs
* in an arbitrary order.
*/
listitems: function Dict_listitems() {
var items = this._state.items;
return [[unconvert(k), items[k]] for (k in items)];
},
/**
* Returns an iterator over all the keys in the dictionary in an arbitrary
* order. No guarantees are made about what happens if the dictionary is
* mutated during iteration.
*/
get keys() {
// If we don't capture this._state.items here then the this-binding will be
// incorrect when the generator is executed
var items = this._state.items;
return (unconvert(k) for (k in items));
},
/**
* Returns an iterator over all the values in the dictionary in an arbitrary
* order. No guarantees are made about what happens if the dictionary is
* mutated during iteration.
*/
get values() {
// If we don't capture this._state.items here then the this-binding will be
// incorrect when the generator is executed
var items = this._state.items;
return (items[k] for (k in items));
},
/**
* Returns an iterator over all the items in the dictionary as key-value pairs
* in an arbitrary order. No guarantees are made about what happens if the
* dictionary is mutated during iteration.
*/
get items() {
// If we don't capture this._state.items here then the this-binding will be
// incorrect when the generator is executed
var items = this._state.items;
return ([unconvert(k), items[k]] for (k in items));
},
/**
* Returns a String representation of this dictionary.
*/
toString: function Dict_toString() {
return "{" +
[(key + ": " + val) for ([key, val] in this.items)].join(", ") +
"}";
},
/**
* Returns a JSON representation of this dictionary.
*/
toJSON: function Dict_toJSON() {
let obj = {};
for (let [key, item] of Iterator(this._state.items)) {
obj[unconvert(key)] = item;
}
return JSON.stringify(obj);
},
});