Instance Keywords

Keyword	Description	value
self	The instance which is executing the current block of code.	-1

 

self can be used to identify the calling instance of the current block of code, as it always references the unique ID for the instance currently in scope. For example:

var val = 100;
with (instance_create_layer(x, y, "Instances", obj_Fire))
    {
    self.val = val;
    }

In this example you can see that we have a local variable called val and we want it to set the instance variable with the same name in the newly created object instance. To identify the instance variable correctly and tell GameMaker Studio 2 to set it in the instance calling the code block, we use the self keyword. In most cases you can also use the id built-in instance variable instead of self, but self offers certain benefits. To start with, it is faster for the compiler to retrieve the instance ID value using self rather than id, as the id value goes through the instance lookup table. Secondly, for those people making extensions, it is very useful to ensure the correct scoping of variables, since it is possible that a project which uses an extension may have a global scope variable or something with the same name as a variable in the extension.

It is also worth noting that self can also be used within structs - under very specific circumstances - to reference member variables for the struct.

 

Keyword	Description	value
other	The other instance involved in a collision event, or the other instance from a with function.	-2

 

The special keyword other has two different ways that it can be used to reference a specific instance: when used in a with function (explained here) or when used in a collision event, which is what this section is going to explain.

A collision event can only happen between two instances. You can have multiple collisions between multiple instances, but they are all resolved by GameMaker Studio 2 on a 1-on-1 basis, with the instance that has the collision event and the "other" instance that is involved. Imagine you have a player object, multiple enemy objects and multiple bullet objects that the enemy can fire at you. You can assign each enemy a single bullet instance but with a different damage variable randomly assigned to it when created, for example:

var nnn;
nnn = instance_create_layer(x, y, "Bullets", obj_Bullet);
nnn.damage = 5 + irandom(5);
nnn.speed = 8;
nnn.direction = point_direction(x, y, obj_Player.x, obj_Player.y);

You can see how we set its variables using the "point method" outlined in the section on Addressing Variables In Other Instances. This will give the bullet objects a different damage value. But what about the player object? How will it detect the damage that it has to take? By using other in the collision event:

hp -= other.damage;
if hp <= 0 instance_destroy();

The above code will deduct the amount stored in the other instance in the collisions "damage" variable from the player "hp" variable, then it will check to see if the "hp" is lower than or equal to 0. If it is then it will destroy the player object. Please note that other used in this way only works in the collision event and that the other instance must have the variable being checked or else an error will be thrown. However you can assign values to variables, or even create new ones, using other in the collision event too, like this:

//add ten to the other instance "mana" variable
other.mana += 10;
//set the other instance variable "hit" to true, creating it if the variable doesn't already exist
other.hit = true;

 

Keyword	Description	value
all	All instances currently active in the room.	-3

 

This keyword is used to tell GameMaker Studio 2 that a function is to be applied, or to check, all active instances within a room (deactivated instances will not be checked or accessed). You cannot use all to access or set variables in other instances using the point method (see here), but you can use it when calling with(), for example:

with (all)
    {
    speed = 0;
    }

The above code will set the speed of all instances in the room to 0. You can also use all within functions to target or check all instances in the room for example:

//Check a point for any active instance in the room
inst = instance_position(mouse_x, mouse_y, all);         

//Check all instances for a collision along a line
if collision_line(x, y, mouse_x, mouse_y, all, false, true) {}

//Add all instances in the room into a motion planning grid
mp_grid_add_instances(grid, all, false);

all is a very useful keyword and can be used in numerous situations within your code and actions, often cutting down on the amount of code you need to write to achieve a desired effect.

 

Keyword	Description	value
noone	No instance at all.	-4

 

It may seem odd, but many times while programming your games will you find the need to check if there are no instances found at a location, or in a collision etc... In those cases you would use this keyword to check for nothing, something like this:

if instance_nearest(x, y, obj_enemy) != noone
    {
    //do something as there is an enemy instance near
    }

In this example, the function instance_nearest() will return either noone or the unique ID of the nearest found instance. Basically, any time that you need to check for an instance, you can expect to get either noone or a unique instance ID returned.