Pick the wrong one and it won't even compile.
The problem
This won't compile.
const Vector3 SpawnPoint = new Vector3( 0, 0, 100 );const only works with values known when the code is built, like numbers and strings.
The difference
Built in vs set once.
Both stop a value from changing. They differ in when the value is decided.
- const
- fixed when you compile
- readonly
- set once, at runtime
The fix
readonly for anything you build.
const float Gravity = 800f; static readonly Vector3 SpawnPoint = new( 0, 0, 100 );
Numbers and strings can be const. Anything you construct, like a Vector3, needs readonly.
Also
readonly can be set in a constructor.
class Weapon{ readonly float _damage; public Weapon( float damage ) { _damage = damage; }}
Each weapon decides its damage once. Nothing can change it after.
The rule
Build time: const. Runtime: readonly.
- Numbers, strings
- const
- Vectors, objects
- static readonly
- Per object
- readonly