Access object members from Instance ID

Question

I'm getting the Instance ID of an object from collision_line()

Now that I have this instance, I want to get it's image_angle, but I get an 'unknown variable' message when I try that.

What should I do?

Answer 1

what is the value of this collision_line()? The collision_line() function returns an instance id - however when nothing is found it returns noone (-4).. So you'll have to test for that first:

var inst, imgangle;
inst = collision_line(...);
if (inst != noone) {
    imgangle = inst.image_angle;
    //etc etc
}

or alternativelly (more cleanly in GM), we can "abuse" the with statement. With executes all following code from the perspective of the given instance id (or for all instances of a certain object when given the object id).
However the value noone will automatically prevent any execution.

var inst, imgangle;
inst = collision_line(...);
with (inst) {
    imgangle = image_angle; 
    //note that we do no longer have to put "inst." before getting a variable
    //etc etc
}