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 | [printable version] [offline version] | offline version generated on 04-Aug-2010 21:08 UTC |  |
XDCscript - Map-Object
An ordered hash table type
Contents |
Synopsis
| | var map = someMapObj; map.length; // Gets the number of values in this map. var someVar = map[i]; // Gets an element of this map whose index i is in the range 0..length-1. map[i] = someValue; // Sets an element of this map whose index i is in the range 0..length-1. map[s] = someValue; // Sets a map element given a string-value key s. var someVar = map[s]; // Gets a map element given a string-value key s. // Returns undefined if the designated element does not exist. |
Description
A map is an aggregate that comprises an expandable ordered set of values of some common base type, indexed by strings as well as non-negative integers. Maps are a constrained hybrid of a JavaScript object and array; each map has a length property and map objects can be indexed either by a numeric index or by a string valued key.
Because of JavaScript's type conversion rules, it is not possible to distinguish between map["2"] and map[2]; strings that represent integral numbers are converted to numbers before accessing a map element's value. So, all string keys used to defined elements in a map must be non-numeric.
Unlike JavaScript arrays, maps range check indexes; attempts to index outside the range of defined values results in an error.
| | map = [["zero", 0]]; print(map["one"]); // prints undefined print(map[1]); // ERROR: map has just one element print(map["1"]); // ERROR: same as above |
Examples
Iterating over the elements of a map
Iterating over the elements of a map.
| | /* display elements of map by index */ for (var i = 0; i < Mod.map.length; i++) { print("map[" + i + "] = " + Mod.map[i]); } /* display elements of map by name */ for (var i in Mod.map) { print("map{" + i + "} = " + Mod.map[i]); } |
When iterating of the elements of a map by name, the order is always the same as iterating by index starting from 0.
Deleting a map
Deleting a map.
| | Mod.map = undefined; |
Redefining a map
Redefining a map.
| | Mod.MAP = [ /* redefine a map */ ["one", 1], ["two", 2] ]; |
Deleting elements from a map
Deleting elements from a map.
| | delete Mod.map["two"]; /* delete the "two" element in the map */ |
Adding elements to a map
Adding elements to a map. The special $putHead() and $putTail() operations will add a name-value pair to the head or tail or a map, respectively.
| | if (!"zero" in Mod.map) { Mod.MAP.$putHead("zero", 0); /* add new ["zero", 0] to front of map */ } if (!"zero" in Mod.map) { Mod.MAP.$putTail("zero", 0); /* add new ["zero', 0] to end of map */ } |
The special $putHead() and $putTail() operations will move existing elements to the head or tail, respectively.
| | /* reverse the elements of a map */ for (var k in Mod.map) { Mod.map.$putHead(k, Mod.map[k]);/* move existing element to front of map */ } |
Replacing elements in a map
Replacing elements in a map.
| | Mod.map["two"] = 1; /* redefine the "two" element */ Mod.map[1] = "one"; /* redefine the second element element */ |
| [printable version] [offline version] | offline version generated on 04-Aug-2010 21:08 UTC | |
