Kotlin Design Patterns and Best Practices/

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Strategy Design Pattern

Strategy Design Pattern

Learn how to implement the Strategy design pattern in Kotlin and how it allows an object to alter its behavior at runtime.

We'll cover the following...

Strategy

The goal of the Strategy design pattern is to allow an object to alter its behavior at runtime.

Imagine we’re building a 2D side-scrolling arcade platform game. That is, we have our game character, which we control with arrow keys or a gamepad. Our character can move left, right, and jump. Our character has a lot of enemies, which consist mostly of carnivorous Tanzanian snails.

Canary Michael, who acts as a game designer in our small indie game development company, came up with a great idea. What if we were to give our hero an arsenal of weapons to protect us from those horrible carnivorous snails?

Weapons all shoot projectiles (we don’t want to get too close to those dangerous snails) in the direction our hero is facing. All projectiles should have a pair of coordinates since our game is 2D (as represented in enum class), and a direction:

enum class Direction {
    LEFT, RIGHT
}
data class Projectile(private var x: Int,
           private var y: Int,
           private var direction: Direction)
Defining projectile class

If we were to shoot only one type of ...