Syntactic sugar
Programmers use the term syntactic sugar to refer to special rules that let you write your code in a way that doesn't correspond to the normal rules but that is easier to remember how to do and looks better.
Let's say we want to set the name of a dog. As a starting point, name can be set along with everything else at object creation time, as in example - p050newdog.rb
| class NewDog def initialize(breed, name) @breed = breed @name = name end attr_reader :breed, :name # create reader only end nd = NewDog.new('Doberman', 'Benzy') puts nd.name |
Let's write a set_name method that allows us to set, or reset, the name of an existing dog. We'll also rewrite the initialize method so that it doesn't expect a name:
| class NewDog def initialize(breed) @breed = breed end attr_reader :breed, :name # create reader only # setter method def set_name(nm) @name = nm end end nd = NewDog.new('Doberman') nd.set_name('Benzy') puts nd.name |
Ruby allows you to define methods that end with an equal sign (=). Let's replace set_name with a method called name=
| def name=(nm) @name = nm end |
name= does exactly what set_name did, and in spite of the slightly odd method name, you can call it just like any other method:
nd.name=('Benzy')
Here's the modified example -
| class NewDog def initialize(breed) @breed = breed end attr_reader :breed, :name # create reader only # setter method def name=(nm) @name = nm end end nd = NewDog.new('Doberman') nd.name=('Benzy') puts nd.name |
The equal sign gives you that familiar "assigning a value to something" feeling, so you know you're dealing with a setter method. It still looks odd, but Ruby takes care of that, too.
Ruby gives you some syntactic sugar for calling setter methods. Instead of this
nd.name=('Benzy')
you're allowed to do this:
nd.name = 'Benzy'
When the interpreter sees the message "name" followed by " =", it automatically ignores the space before equal sign and reads the single message "name="-a call to the method whose name is name=, which we've defined. As for the right-hand side: parentheses are optional on single arguments to methods, so you can just put 'Benzy' there and it will be picked up as the argument to the name= method.
Method calls using the equal-sign syntax are common in Rails applications.
