Physics

// PHYSICS CONSTANTS
struct PhysicsCategory {
    static let None       : UInt32 = 0
    static let All        : UInt32 = UInt32.max
    static let player     : UInt32 = 0b1             // 1
    static let bullet     : UInt32 = 0b10            // 2 
}

var nodesToRemove = [SKNode]()

    // #-#-#-#-#-#-#-#-#-#-#-#-#-#-#
    //MARK: - Physic Contact Delegate methods
    // #-#-#-#-#-#-#-#-#-#-#-#-#-#-#
    
    func didBegin(_ contact: SKPhysicsContact) {
        var one: SKPhysicsBody
        var two: SKPhysicsBody
        
        if contact.bodyA.categoryBitMask < contact.bodyB.categoryBitMask {
            one = contact.bodyA
            two = contact.bodyB
        } else {
            one = contact.bodyB
            two = contact.bodyA
        }
        
        // PLAYER AND BULLET
        if one.categoryBitMask == PhysicsCategory.player && two.categoryBitMask == PhysicsCategory.bullet {
           nodesToRemove.append(one.node!) // remove player
           nodesToRemove.append(two.node!) // remove bullet
        }
    }
    override func didFinishUpdate()
    {
        nodesToRemove.forEach(){$0.removeFromParent()}
        nodesToRemove = [SKNode]()
    }
}