How to detect objects within a radius without using a trigger collider?

Question

I want an object to run code that detects objects around them, in a specific radius.

BUT I cannot use a trigger... or any game objects or components.

What could I do just using code?

Answer 1

The classes Physics and Physics2D contain several useful static methods to detect Colliders and Collider2Ds within geometric shapes. For example, if you want to get all objects overlapping a sphere with radius 10 around the current gameObject you would do this:

 var colliders = Physics.OverlapSphere(transform.position, 10f)
 foreach(var collider in colliders) {
       Debug.Log($"{collider.gameObject.name} is nearby");
 }

Most of these methods also have "NonAlloc" variants which overwrite an existing array instead of creating a new one. These methods are faster and generate no garbage (especially if you call them a lot), but are a bit harder to use and require that you know an upper limit of how many objects you are going to detect at most.