Understanding the initialize method

When you create a new class in Pharo (for example, a class representing an agent, a cell, or a model in Cormas), that class can have a special method called initialize. This method is used to set up your object when it is first created and to assign default values to its attributes.

What is initialize?

Every time you create a new object in Pharo, it's born empty - it doesn't yet know what values it should have. The initialize method is where you give your new object its first settings.

Example

Duck

initialize
    super initialize.
    energy := 50.
    state := #baby

Here, we make sure that every instance of a Duck will have energy 50 and state #baby. When Pharo creates a new Duck, it automatically calls this method.

Why we always write super initialize

If your class inherits from another one (for example, Duck inherits from CMAgent), then that parent class might also have some important setup to do. To make sure that setup is not lost, we always call:

super initialize.

It means: "Run the initialize method of my parent first, then do my own setup."

If you forget to add super initialize, your object might not work correctly - it could miss important data from its superclass.

Example of what can go wrong

Duck

initialize
    energy := 50

If the superclass (CMAgent) defines things like its position or size in its own initialize method, skipping super initialize means your duck agent will be missing that information!

So remember:

tip

Always start your initialize method with super initialize.

When initialize is called

In Pharo, initialize is automatically called when you create a new instance using:

Duck new

This automatically runs:

1. The initialize of all superclasses (through super initialize),
2. Then your class's own initialize.

You don't have to call it yourself - Pharo does it for you.

Difference between Pharo's initialize and Cormas' init methods

Cormas uses its own special init methods, such as initBigForest, initUrbanArea, etc., to prepare a model for simulation. These are not the same as Pharo's initialize.

Purpose	When It Runs	Example
initialize	When you create a new object (like an agent, cell, or model).	duck := Duck new.
Cormas init methods	When you start or restart a simulation scenario	self initBigForest.

Think of it like this:

• initialize gives life to a new object (sets its default values).
• init prepares your whole model world before running the simulation.

You can define an initialize method in any class, but there can be only one initialize method per class. In contrast, init methods are defined only in the model class, and it can contain several different init methods for different initialization scenarios.

Example from a Cormas model

Let's look at how both methods might appear together. First, we add an initialize method to Duck class, defining the default energy and state values for each new duck.

Duck

initialize
    super initialize.
    energy := 50.
    state := #baby

Then we add an initialize method to DuckModel class setting the default value for the numberOfDucks attribute.

DuckModel

initialize
    super initialize.
    numberOfDucks := 10

Finally, we create an initForest method defining the initial configuration for the simulation. It will create 10 ducks, each duck will have energy = 50 and state = #baby (createN:entity: method creates new ducks with Duck new and that method executes our initialize).

DuckModel

initForest
    <init>
    self createN: numberOfDuck entity: Duck

Key takeaways

• initialize is called automatically when an object is created.
• Always include super initialize at the beginning.
• Use initialize for setting default values of your object.
• Use initScenario, initSimulation, or similar in Cormas to prepare the model world.
• Don't mix the two - initialize is for objects; init is for model setup.