JASS

Article on other languages:

del.icio.us del.icio.us
Digg Digg
Furl Furl
Reddit Reddit
Rojo Rojo
Add to OnlyWire
This article is about the programming language. For the Vietnamese charity, see Japanese Association of Supporting Streetchildren.

JASS, J-Asynchronous Scripting Syntax[citation needed] , is an event driven scripting language used in Blizzard Entertainment's Warcraft III game. Map creators can use it in the World Editor to create triggers and AI scripts.

Contents

Features

The language provides an extensive API that gives programmers control over nearly every aspect of the game world. It can, for example, give orders to units, change the weather and time of day, play sounds and display text to the player, and manipulate the terrain. It has a syntax similar to Turing and Delphi, although, unlike those languages, it is case sensitive. JASS primarily uses procedural programming concepts, though popular user-made mods to Blizzard's World Editor program have since added C++-like object-oriented programming features to JASS's syntax.

Sample code

The following function creates a string containing the message "Hello, world!" and displays it to all players:

function Trig_JASS_test_Actions takes nothing returns nothing
 call DisplayTextToPlayer(GetLocalPlayer(), 0, 0, "Hello, world!")
endfunction

or if you want this only for one player:

function Trig_JASS_test_Actions takes player p returns nothing
 call DisplayTextToPlayer(p, 0,0, "Hello, world!")
endfunction

And if you want to print the message 90 times and show the iterator:

function Trig_JASS_test_Actions takes player p returns nothing
 local integer i=0
 loop
   exitwhen i==90
   call DisplayTextToPlayer(p, 0,0, "Hello, world! "+I2S(i))
   set i=i+1
 endloop
endfunction

Basic Syntax

JASS's syntax is similar to Turing. It is context free. Examples of basic syntax are shown below:

function syntax_Example_Sum takes integer i, real r returns real //function declaration must include: the keyword "function", 
                                                                 //the function name, parameters (if any) and return type (if 
                                                                 //it returns something)
  return i + r //return statements must begin with the keyword "return"
endfunction //the keyword "endfunction" signals the end of a function block

function syntax_Example takes nothing returns nothing 
  local integer i //declaring a local variable requires the modifier "local", the variable's data type, and the variable name
  local real r = 5.0 //local variable declarations must come before anything else in a function and variables may be 
                     //initialized on declaration

  //separated statements MUST be placed on separate lines

  set i = 6 //the keyword "set" is used to rebind variables
  call syntax_Example_Sum( i, r ) //function calls must be preceded by the keyword "call"
  set r = syntax_Example_Sum( i, r ) //the "call" keyword is omitted when accessing a function's return value
endfunction

Types

JASS is statically-typed, and its types can be separated into two classes: natives and handles. The native types are:

  • integer (32-bit signed)
  • real (32-bit floating point numbers, similar to the float type in Java)
  • boolean
  • code

All other types are considered non-native. The native types behave very similarly to primitive types in other programming languages. Handle types, however, behave more like objects. Handle types often represent an "object" within the game (units, players, special effects, etc.). Similarly to how Java treats Objects, all variables and parameters in JASS of handle types are treated as values, but in reality those values are nothing but references to the handle objects. This becomes important when dealing with garbage collection because handles, if not properly cleaned up, can cause significant performance issues. Additionally, any references to handles themselves take up memory space and if they are not nullified can also reduce performance, though on a much smaller scale.

function garbage_Collection_Example takes string effectPath, real x, real y returns nothing
 local effect specialEffect = AddSpecialEffect( effectPath, x, y ) //uncleaned handle types will continue to take up system resources
endfunction

function garbage_Collection_Example2 takes string effectPath, real x, real y returns nothing
 local effect specialEffect = AddSpecialEffect( effectPath, x, y )
 
 set specialEffect = null //setting the variable to null is not enough, since it is only a reference to the handle; 
                          //the handle still exists
endfunction

function garbage_Collection_Example3 takes string effectPath, real x, real y returns nothing
 local effect specialEffect = AddSpecialEffect( effectPath, x, y )
 
 call DestroyEffect( specialEffect ) //we destroy (clean up) the handle to free up memory
 set specialEffect = null 
endfunction

function garbage_Collection_Example4 takes effect e returns nothing
  //do stuff
  call DestroyEffect( e )
  //parameters do not have to be nullified
endfunction

Another property of handle types worth noting is that all handle types are treated as if they were children of the "handle" type. Some of these children types have their own children types, and so on. Handle variables may reference its own specific handle type or any children type. For example:

function Trig_JASS_handle_Example_Child takes widget w, widget w2 returns nothing
  //do stuff
endfunction

function handle_Example takes real x, real y returns nothing
  local widget w //widget is a handle type with children type unit and destructible
  local unit u = CreateUnit( 'hfoo', x, y )
  local destructible d = CreateDestructible( 'ATtr', x, y )
  
  set w = u //acceptable
  call Trig_JASS_handle_Example_Child( w, d ) //acceptable
endfunction

Type Casting

Of the primitive types, type casting between integer, real, and string is officially supported by the language. JASS supports both implicit and explicit type casting.

Implicit casting only occurs from real to integer. For example:

function type_Casting_Example takes nothing returns real
  local integer i = 4
  local real r = 5 //implicit cast of 5 to real to satisfy variable type
  
  if ( i < r ) then //implicit cast of i to real
    set r = r / i //implicit cast of i to real in order to carry out real division
  endif
  
  return i //XXX: NOT allowed; JASS does not allow implicit casting from integer to real to satisfy return types
endfunction

The JASS library provides several functions for explicit type casting:

  • I2R(): casts integer to real
  • R2I(): casts real to integer
  • I2S(): casts integer to string
  • R2S(): casts real to string

An important property of handle types related to type casting is that since all variables of handles are just references, they can all be treated (and are treated) as integers. Each instance of a handle is assigned a unique integer value that essentially acts as an identifier for the handle. Therefore, type casting from handles to integers, although technically not supported by JASS, is possible in practice because implicit casting from handle types to integer can and will occur if the code is written in a certain way, for example:

function H2I takes handle h returns integer
  return h
endfunction

If the game ever reached the line "return h", it would in fact actually cast the handle to an integer and return the value. However, Blizzard never intended for JASS to be used this way, and so the JASS compiler will actually throw an error, warning the programmer that the function isn't returning the correct type. However, JASS programmers have found and exploited a now famous bug in the JASS compiler's syntax checker: the so-called "return bug". Essentially, the compiler will only make sure that the last return statement in a function returns the correct type. Therefore, the following code compiles without error and can be used to cast handles to integers

function H2I takes handle h returns integer
  return h //the function will stop executing after the first return statement, i.e. this one
  return 0 //the compiler will only check this statement for syntax accuracy, but it is in reality unreachable code
endfunction

Arrays

Java supports one-dimensional arrays of any type. The syntax to declare arrays and access members in an array is outlined in the code below.

function array_Example takes nothing returns nothing
  //arrays cannot be initialized at declaration and their members will hold arbitrary values
  local integer array numbers
  local unit array units
  local boolean array booleans
  local integer i = 1
  
  set numbers[0] = 1 //the syntax to initialize an array member is identical to that for any other variable, only a set of 
                     //brackets: [] must immediately follow the variable name with the index value of the specific member
                     //to initialize inside the brackets
  set units[0] = CreateUnit( 'hfoo', 0, 0 ) //indexes for arrays always start at 0
  
  loop
    exitwhen ( i > 8191 ) //the maximum size for arrays in JASS is 8192, which means that the last index of any array can 
                          //only be 8191
    set numbers[i] = i    //variables can substitute for constants when specifying the index value in the brackets
    set units[numbers[i]] = null //array members can also substitute
    set boolean[i-1] = true //arithmetic (or functional) operations are also acceptable
  endloop

  if ( boolean[200] == true ) then //to access an array member, again the syntax is the same as for normal variables, only 
                                   //with the addition of the brackets with the index value inside
    set numbers[200] = -200 //you can re-assign members of the array to different values
  endif
endfunction

One limitation of arrays in JASS is that they cannot be returned by functions or passed as parameters to other functions, though array members may be returned (in a function that returns a unit, u[0] may be returned if u is an array of type unit).

vJASS

vJASS is a set of user-made extensions to JASS. It introduces object-oriented programming features to the language, such as structs, encapsulation, and polymorphism.[1] Strictly speaking, vJASS does not add anything to the JASS library but instead mostly uses JASS's own arrays and type casting to integers. The extension relies on a custom-made compiler that compiles vJASS code to strict JASS code. In this manner, no additional mods for either the World Editor program or Warcraft III are required, and maps made using vJASS code are fully compatible with any copy of the game, even those without the compiler.

References

  1. ^ vJASS Documentation

External links

Documentation

  • An Introduction To JASS--A beginner's guide to the language, covering its basic features and capabilities.
  • JASS Manual--An advanced guide to the language, intended to serve as a reference for users who are already proficient with it. Includes a comprehensive API browser.
  • Wc3jass Tutorials--A collection of tutorials about the language.
  • wc3c JASS Tutorials--Other tutorials about the language.

Communities

Scripts

Tools

The Warcraft series and related topics
Games
Books
Professional
Competition
Other
Retrieved from "http://en.wikipedia.org/wiki/JASS"

This article is from Wikipedia. All text is available under the terms of the GNU Free Documentation License.

Giant Panda

Mercedes Car
James Bond Guide
This site monitored by SitePinger.net