JS OOP trouble

Question

i have a script called skills.js :

class Skill { var damage: float; var rate : float; var hits : int; var selected : boolean; var name : String;

 function Skill(nam : String, dmg : float, rat : float, hit : int, sel : boolean){
     this.damage = dmg;
     this.rate = rat;
     this.hits = hit;
     this.selected = sel;
     this.name = nam;
 }

}

punch = new Skill("punch", 5, 0.2, 1, false); slash = new Skill("punch", 3, 0.1, 1, false); headbutt = new Skill("punch", 8, 1, 1, false); push = new Skill("punch", 2, 0.6, 1, false); ` and i want to access the it's values properties in another script. for example in player.js:

var damage = skillScript.punch.damage;

but is won't let me and it returns as a log warning when ever i start the game up. if somebody knows what i need to do please help. thanks for reading and here is the error if it helps:

NullReferenceException: Object reference not set to an instance of an object Boo.Lang.Runtime.RuntimeServices.GetDispatcher (System.Object target, System.String cacheKeyName, System.Type[] cacheKeyTypes, Boo.Lang.Runtime.DynamicDispatching.DispatcherFactory factory) Boo.Lang.Runtime.RuntimeServices.GetDispatcher (System.Object target, System.Object[] args, System.String cacheKeyName, Boo.Lang.Runtime.DynamicDispatching.DispatcherFactory factory) Boo.Lang.Runtime.RuntimeServices.GetProperty (System.Object target, System.String name) UnityScript.Lang.UnityRuntimeServices.GetProperty (System.Object target, System.String name) player.FixedUpdate () (at Assets/Scripts/player.js:54)

Answer 1

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Answer by aldonaletto · Aug 07, 2011 at 12:00 AM

It seems you want punch, slash etc. to be global variables. The equivalent to global in Unity is static - you must declare them this way:

static var punch = new Skill("punch", 5, 0.2, 1, false);
static var slash = new Skill("punch", 3, 0.1, 1, false);
static var headbutt = new Skill("punch", 8, 1, 1, false);
static var push = new Skill("punch", 2, 0.6, 1, false);

You can access these globals in other scripts using the script name:

  var damage = skills.punch.damage;

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dick · Aug 07, 2011 at 01:01 PM 0

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thanks it works like magic

Peter G · Aug 07, 2011 at 02:31 PM 0

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That is actually incorrect. Static is NOT global. Static makes a variable a class variable as opposed to an instance variable. The following line is perfectly legal, but is not a global variable:

  private static var punch = ...;

only the public modifier makes a variable global (its the default in js). Static has nothing to do with the variable's accessibility level.

aldonaletto · Aug 07, 2011 at 03:03 PM 0

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I don't think global is the same as public: a public variable has script scope - it only exists inside the script - while the global has program scope. The definition of global variable is "a variable that has program scope", which means that it's known by everybody in the program and keeps its contents while the program exists. Isn't the same behaviour of a static variable? Ok, both may be implemented in different ways, but that's why I said "the equivalent to global in Unity is static". I really would love to know how they implement static vars - if old fashioned globals, or as properties of a commom class - but the effect is the same.

SisterKy · Aug 07, 2011 at 03:54 PM 0

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@Peter G Wait, are you saying the public keyword alone is sufficient to make a var a global or are you saying public + static keywords make a global?
Would you call the first of these two a global?

 public var punch = ...;
 public static var punch = ...;

So far, I had been under the impression static was enough to define a global, but I'd have no problem to learn that public static is required. But only public...? now that would break my view of the world...? :p

Peter G · Aug 07, 2011 at 10:21 PM 1

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@Sister$$anonymous$$y, for starters, you have to understand that Unityscript, although it has different syntax, has many similarities to C#/.Net that web js doesn't have such as strong and static typing. It also implicitly does classes as opposed to prototyping. So when I reference C#, its because that unity script behaves the same way.

C++ allowed you to create variables outside of classes which C# does not. That is a global variable in C/C++. So in a sense, you can't ever get to that scope using js or C# which is probably a good thing because it can make it difficult to debug. As @aldonaletto says, the closest you can get to this behavior is to use a public static variable which is accessible on all levels and exists for as long as the assembly of the containing class is loaded.

Around here, a lot of the time, people will refer to global variables as simply being public.

@aldonaletto, I agree with your latest comments with one small exception. I wouldn't call it script scope. It's a matter of ter$$anonymous$$ology, but its usually defined as being accessible from only within the class. The differentiation from script scope is that you can have multiple classes defined in a single file. Here's the msdn page on the private access modifier.

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