Unity Crashes when i attach script to object

You need to keep the scope of the class together, you defined the class and the constructors in different scopes. I'm also not sure if overWorld extends/inherits/derives from MonoBehaviour. It should to be attached to a game object in the inspector

 public class weapon extends overWorld
 {
     public var ammo : int;
     public var damage : int;
     public var numberOfBullets : int;
     public var firetype : int;
     public var range :int;
     public var weaponType : weaponTypes;
 
     // Parameterless constructor of class weapon
     public function weapon()
     {
         ammo = 0;
         damage = 0;
         numberOfBullets = 0;
         firetype = 0;
         range = 0;
         weaponType = weaponTypes.pistol;
     }
 
     // Parameterized constructor of class weapon
     public function weapon(amm : int, dmg : int, numOfBullets : int, rateOfFire : int, rng : int, wpnType : weaponTypes)
     {
         ammo = amm;
         damage = dmg;
         numberOfBullets = numOfBullets;
         firetype = rateOfFire;
         range = rng;
         weaponType = wpnType;
     }
 
     // I'm assuming the scope of this, you will again access outside of the cass with weapson.weapsonTypes.sword for example
     public enum weaponTypes
     {
         sword,
         pistol,
         shotgun,
         machinegun,
         semiauto,
         sniper,
     }
 }
 
 public var sniper : weapon = new weapon(5, 5, 5, 1, 5, weaponTypes.sniper);