Actors & Classes

What's the difference?

In Pony, logic inside a class is run synchronously, whereas actors are run with asychronous communication.

Actors replace threads for concurrency.

Constructors

Constructors are defined by the new keyword:

new my_constructor([args]) =>
    ...

An actor or class can have multiple constructors with different names.

Default constructor

The default constructor for an agent or class is create:

actor Main
    new create([args]) =>
        ...

Instantiating

You instantiate a class or actor like so:

my_variable = ClassOrActor

another = ClassOrActor(with_argument)

Fields

Fields are defined as such:

var _field: Type

new create() =>
    ...

The underscore before the field's name denotes it as being private. In this case we don't assign a value to the field, and so the code won't compile unless we assign it a value in the constructor.

Return Types

When defining behaviours or functions, specifying the return type is important. If no return type is specified, then the compiler will assume that the function returns a None type.

Classes

Functions

In classes, functions are defined like so:

fun ref function_name(): ReturnType =>
    ...

apply function

The apply function is meant to implement some common functionality of a class, and can be called directly. For example:

class ExampleClass
    fun apply(var_one: String, var_two: String)
        ...

my_class = ExampleClass
result = my_class("String one", "String two")

As you can see you don't need to call my_class.apply("String one", "String two"), and you can just omit .apply.

Actors

Behaviours

In actors, rather than defining functions, you define behaviours using the be keyword:

be behaviour_name(): ReturnType =>
    ...