Classes in Eia

Eia supports adding external class and lets you access its public functions and variables. You may import an external class as a static or an instantiated object.

Defining Classes

So how do you define a class?
It's really simple, just add visible modifier to global variables and functions to make it visible to other classes.

visible fn sayMeow() {
  println("Meow!")
}

By default, all the variables and functions are marked private.

Constructors

In Eia, you may add an object constructor by defining a visible init with desired arguments. You may define multiple of init functions with varying number of arguments.

init() function is not required if you are accessing a class statically

// Global visible variables that stores a person^s name and their age
// Variables initially nil (null)
 
visible var person: String = nil
visible var age: Int = nil
 
visible fn init(name: String) {
  person = name
  age = 20  // default age
}
 
visible fn init(name: String, _age: Int) {
  person = name
  age = _age
}
 
visible fn printUser() {
  println(format("Person named %s of age %d", person, age))
}

Including an external class

You can include an external class using include keyword. E.g., including Person.eia which lies in the same directory (simulation).

include(
  "simulation/Person"
   ...
)

If a path

1. Starts with /, Eia assumes it's a full path.
2. Doesn't start with /, it appends user directory at the beginning.
3. Starts with prefix stdlib, it is replaced by path of standard library directory.

Creating objects

new keyword is used to create an instance of a class:

// Create an instance of Person using either init(name: String)
// or init(name: String, age: Int)
 
let person = new Person("Melon", 16)
person.printUser()
println(person.age)

It prints the following:

Person named Melon of age 16
16

Static usage of a class

Consider this file:

include(static:std:string)
 
var lastNTimes = 0
 
visible fn sayMeow(nTimes: Int) {
  nTimes += lastNTimes
  println("Meow ".repeat(nTimes))
}

Now, to use this file statically, we'll import it:

include(static:"simulation/Cat.eia")

then we use it:

println(sayMeow(2))
println(sayMeow(3))

this outputs the following:

Meow Meow
Meow Meow Meow Meow Meow

Tips

In Eia you can implement a string() function to return a custom text:

visible fn string(): String {
  return "Person(name=" + person + ", age=" + age + ")"
}

now when you do:

let person = new Person("Melon", 16)
println(person)

you would see:

Person(name=Melon, age=16)