Structs are copied. Here's what that means.
The problem
It won't even compile.
List<Vector3> path = GetPath(); path[0].y = 5f;// error CS1612: Cannot modify the return value// because it is not a variable
Vector3 is a struct. The list hands you a copy, and editing a temporary copy would do nothing.
Why it happens
Classes share. Structs copy.
Assigning a class gives you the same object. Assigning a struct gives you a new copy.
- class
- both names point to one object
- struct
- each name has its own copy
The fix
Copy out, change, put back.
var p = path[0];p.y = 5f;path[0] = p;
Take the copy, change it, and write it back into the list.
The sneaky version
It compiles, and does nothing.
var target = enemy.WorldPosition;target.z += 100f;// enemy hasn't moved! enemy.WorldPosition = target;
Changing a copy compiles fine. Nothing moves until you assign it back.
The rule
Changed a struct? Assign it back.
- In a list
- copy, edit, write back
- A position
- assign it back
- Vector3, Rotation
- structs