User Guide #27 - Ruby - Object initialization

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Our Fruit class from the previous chapter had two instance variables, one to describe the kind of fruit and another to describe its condition. It was only after writing a custom

inspect

The

initialize

method

Whenever Ruby creates a new object, it looks for a method named

initialize

initialize

inspect

ruby> **class Fruit**
    |**def initialize**
    |**@kind = "apple"**
    |**@condition = "ripe"**
    |**end**
    | **end**
**nil**
ruby> **f4 = Fruit.new**
**"a ripe apple"**

Changing assumptions to requirements

There will be times when a default value doesn't make a lot of sense. Is there such a thing as a default kind of fruit? It may be preferable to require that each piece of fruit have its kind specified at the time of its creation. To do this, we would add a formal argument to the

initialize

new

initialize

ruby> **class Fruit**
    |**def initialize( k )**
    |**@kind = k**
    |**@condition = "ripe"**
    |**end**
    | **end**
**nil**
ruby> **f5 = Fruit.new "mango"**
**"a ripe mango"**
ruby> **f6 = Fruit.new**
**ERR: (eval):1:in `initialize': wrong # of arguments(0 for 1)**

Flexible initialization

Above we see that once an argument is associated with the

initialize

ruby> **class Fruit**
    |**def initialize( k="apple" )**
    |**@kind = k**
    |**@condition = "ripe"**
    |**end**
    | **end**
**nil**
ruby> **f5 = Fruit.new "mango"**
**"a ripe mango"**
ruby> **f6 = Fruit.new**
**"a ripe apple"**

You can use default argument values for any method, not just

initialize

Sometimes it is useful to provide several ways to initialize an object. Although it is outside the scope of this tutorial, ruby supports object reflection and variable-length argument lists, which together effectively allow method overloading.