The Type System

Learn the core idea with values in Zeile — types.

In Zeile, every value has a type. Variables are representations of values, so they also have types.

Basic Types

There're four basic types in Zeile:

• Int: Integers, such as 0, 42, -100.
• Float: Numbers with fractional component, also known as floating-point numbers, such as 3.14159, -0.1, 3.0.
• String: Texts, such as "Hello!", "123", "😋".
• Bool: Boolean, which is either false or true.

A variable's type is its initial value's type. For example:

let hello = "Hello!"
// The variable “hello” has the type “String”

let myNumber = 42
// The variable “myNumber” has the type “Int”

Other Types

Beside the basic types, other types can represent more information. For example, Character is also a type.

let kasumi = Character.kasumi
// The variable “kasumi” has the type “Character”

let coolSoyo = Character(id: 39, live2d: "039_live_event_289_ur")
// The variable “coolSoyo” also has the type “Character”

Using Types

Let's start from calling say. We call clauses that perform specific tasks a function. A function may take some inputs, we call them arguments. For example, in this code:

say("Hello!", by: .soyo)

We're calling a function named say, "Hello!" and .soyo are arguments passed into the function. by is the label of the second argument.

A function always takes arguments with specific types in order. Different functions may have the same name, but there argument count, type, or label are different. We use a expression like this to uniquely refer to a function:

say(_: String, by: Character)

In this expression, say is the name of the function. The first argument should be a String, and has no argument label, we use an underscore(_) to represent this. The second argument should be a Character, and has an argument label by.

The value you passed into a function as an argument must match the type defination. This line of code below is invalid:

say(1, by: .soyo) // Cannot convert value of type 'Int' to expected argument type 'String'

Creating Values from Types

When you're writting something like “calling a type”, you're actually calling a special function that creates a value of this type. We call this kind of functions initializers.

Character(id: 39)

This line of code calls an initializer of the type Character, which creates a value of this type. This is actually an abbreviation, we're omitting the .init in this call.

Character.init(id: 39)

This line of code does the exactly same thing as the previous code.

When Zeile is inferring the type for you, you have to type the .init explicitly:

say("Hello!", by: .init(id: 39))
// Or, if you don't like this abbreviation
say("Hello!", by: Character(id: 39))