70 lines
2.5 KiB
Markdown
70 lines
2.5 KiB
Markdown
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---
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title: "Magic Values"
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date: 2019-05-23T15:51:58-07:00
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weight: 25
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---
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Our code right now is violating one more good architecture principle.
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```ts
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if (love.keyboard.isDown("up")) {
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const message = this.emit_component_message(MotionMessage, player_one_position_component);
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message.x = 0;
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message.y = -10;
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}
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```
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*Magic values* refer to numbers that have been placed directly in the code. The values being set to *message.x* and *message.y* above are magic values. Why are magic values bad?
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Magic values introduce the possibility of duplication. Let's say I start adding my code to be able to move paddles down. Now I have to change the numbers in two different places. If I ever change one without changing the other, I have introduced a bug.
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There's another reason to avoid magic values too. Suppose I haven't looked at the InputEngine for a while, but I suddenly decide that the paddles are moving too slow. Intuitively, I would want to look for a Component that contains those values, but instead, they would be hidden in the InputEngine. This isn't what you would really expect - why would Input have anything to do with the speed of the paddles?
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Organizing your information consistently is crucial to being able to easily find things that you need to change. You'll thank yourself later.
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Let's make a new Component.
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Create a file: **game/components/paddle_move_speed.ts**
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```ts
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import { Component } from "encompass-ecs";
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export class PaddleMoveSpeedComponent extends Component {
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public y: number;
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}
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```
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And let's add it to our paddle Entity.
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In **game/game.ts**
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```ts
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const move_speed_component = paddle_entity.add_component(PaddleMoveSpeedComponent);
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move_speed_component.y = 10;
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```
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Now let's tell our InputEngine to use it, and why don't we go ahead and make the "down" key move the paddle downward too.
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```ts
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...
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if (player_one_entity) {
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const player_one_position_component = player_one_entity.get_component(PositionComponent);
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const player_one_move_speed_component = player_one_entity.get_component(PaddleMoveSpeedComponent);
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if (love.keyboard.isDown("up")) {
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const message = this.emit_component_message(MotionMessage, player_one_position_component);
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message.x = 0;
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message.y = -player_one_move_speed_component.y;
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} else if (love.keyboard.isDown("down")) {
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const message = this.emit_component_message(MotionMessage, player_one_position_component);
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message.x = 0;
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message.y = player_one_move_speed_component.y;
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}
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}
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...
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```
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I'm starting to get get a bad feeling about this. Are you? Let me explain.
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