Is there a simple replacement for a static variable?

Questions & Answers
1

So I’m using a key unlock system with a static boolean and then setting it to true and false via events, but my teacher hates static variables and calls them lazy and tends to mark me down for them, on the rare occasion I do use them.
So my example is:

static var unlockDoor : boolean;
public var objectToDestroy : GameObject;

function Start () {
	unlockDoor = false;
}

function OnTriggerEnter(other:Collider){
	if(other.gameObject.tag == "Player" && unlockDoor == true){
		Destroy(objectToDestroy);	
		unlockDoor = false;
	}
}

And then I would unlock the door by doing this:

function OnTriggerEnter(other : Collider){
	if(other.gameObject.tag == "Player"){
		buttonUnlock.unlockDoor = true;
		Destroy(this.gameObject);

	}
}

What other alternatives are there? ( I’ve tried some and none work as simple as this does)

2

There’s a reason the keyword exists. You’re free to use static where applicable. :slight_smile: What your teacher hates probably isn’t the use of “static” in general, but using it in lieu of a proper instance variable, parameter passing or reference keeping. In that case its use IS lazy and indicates bad design.

For your example, the unlockDoor boolean should NOT be static, because it means the variable will be untied to any particular instance of your door, and will instead be a general property whose value holds for all doors. Setting “buttonUnlock.unlockDoor = true” then means ALL doors become unlocked, which defeats the purpose of manipulating this variable in OnTriggerEnter.

You should instead make either of the following:

  1. A private boolean variable
    (non-static) called “locked”, which
    is set to true or false in two
    methods, called “Lock” and “Unlock”.
    These methods should be public, so
    you can call them on the door
    instance.

  2. A public boolean property called
    Locked which exposes get/set
    methods. You would then set its
    value with syntax similar to the
    static, but again, on the INSTANCE
    of the door object.

An example of a variable whose value it is perfectly fine to keep static is Unity’s own Mathf.PI, see the documentation:

The value of PI is constant and equal to 3.14… and is not a property whose value defines the state of any particular individual object. Such a variable is a natural static.

3

It’s kind of difficult to answer you question, as it is a design question, and without a better understanding of the system all I can give you is some best practice pointers.

A static variable is a variable which lives outside the context of an instance. For example, the constant PI, or any of the Mathf class methods. None of those things are logically related to a single instance of Mathf.

In your case however, a door’s lock state can be definitely tied to an instnace, or a specific door. Consider this, you have your Door class, this class defines “a door”. However, if you want to define a specific door, you’ll refer to it’s instance rather than it’s class - “the blue door is a door”, the which is answered by “the blue door” - the instance, while the what is answered by “a door” - the class.

In such case, defining unlockDoor as static is wrong, and bad, because you’re using a static variable as a global, which is what get’s people really worked over.

A better definition would be like so:
A door can be either locked or unlocked. A locked door is opened using a specific key:

class Door
{
    bool isLocked;
    string keyType;
}

The player has a keyring, which holds all of his keys:

class Player
{
    Keyring doorKeys;
}

A keyring holds all of the keys the player has acquired. A keyring can be checked to see if it contains a required key:

class Keyring
{
    string[] keys;

    bool HasKey( string keyType );
}

When the player reaches a door, he checks the lock type on the door ( it’s a blue door lock, it’s a small door lock, etc… ), he then checks his keyring for the appropriate key, and if his keyring contains the right key, he will use it to unlock the door:

OnTriggerEnter( Collider other )
{
    Door door = other.GetComponent< Door >();

    // Make sure the trigger is actually a door trigger
    if ( door != null )
    {
        string keyType = door.keyType;  // Check the door's key type
        if ( keyring.HasKey( keyType ) )
        {
            door.Unlock()
        }
    }
}