58 lines
2.2 KiB
Markdown
58 lines
2.2 KiB
Markdown
# Custom object types
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Touch Develop docs for the @boardname@.
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### What is an object?
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An object allows you to bundle several related pieces of data. For instance, if you have a player on the screen, there are two pieces of data that make up the object: its `x` position, and its `y` position. Therefore, we will define a player to be an *object* with two *fields*: the `x` field and the `y` field. By grouping related variables together in a single object, you reduce confusion in your script and eliminate some errors.
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### What is an object type?
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In order to use objects, we must first define an object type. More concretely, in order to create a new player, we must define what a player *is*. In our case, the type of players is the type of objects with two fields `x` and `y` of type `Number`.
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Creating an object type is done in the following manner. Hit "add new", then hit "object type".
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(picture foobar2)
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WARN: unknown picture: foobar2
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You can change the name of the type by clicking on it (i.e. replace `Thing` with `Player`). You can also add two fields of type number. Once this is done, here's what you should see.
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We have now defined what a player is (it has an `x` field and a `y` field). `Player` is a type, just like `Number` and `String`. However, we have not created any player yet.
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### Creating objects and using them
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To create a new *variable* of a given type, you can call the `create` operation on `Player`.
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```
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let p = new Player()
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```
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Just like `var x := 3` creates a new variable (`x`) of type `Number`, the line above creates a new variable (`p`) of type `Player`. We say that `p` is an *instance* of `Player`.
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If you want to *modify* (mutate) `p`, here's how you do it.
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```
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p.x = 5
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```
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You can read the *fields* of `p` as follows.
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```
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basic.showString("My player is at x = ", 150)
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basic.showNumber(p.x, 150)
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```
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That is, the generic syntax for accessing a field `x` of an object `p` is `p → x`.
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If there are multiple players in your game, you may want to create a collection of them.
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```
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let c = (<Player[]>[])
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c.push(new Player())
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```
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A good example of using objects is in the game pac-man runaway. Search for it, read it and clone it!
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