What if we want to say “Hello” a lot without getting our fingers all tired? We need to define a method!

irb(main):010:0> def hi
irb(main):011:1> puts "Hello World!"
irb(main):012:1> end
=> :hi

The code def hi starts the definition of the method. It tells Ruby that we’re defining a method, that its name is hi. The next line is the body of the method, the same line we saw earlier: puts "Hello World". Finally, the last line end tells Ruby we’re done defining the method. Ruby’s response => :hi tells us that it knows we’re done defining the method. This response could be => nil for Ruby 2.0 and earlier versions. But, it’s not important here, so let’s go on.

The Brief, Repetitive Lives of a Method

Now let’s try running that method a few times:

irb(main):013:0> hi
Hello World!
=> nil
irb(main):014:0> hi()
Hello World!
=> nil

Well, that was easy. Calling a method in Ruby is as easy as just mentioning its name to Ruby. If the method doesn’t take parameters that’s all you need. You can add empty parentheses if you’d like, but they’re not needed.

What if we want to say hello to one person, and not the whole world? Just redefine hi to take a name as a parameter.

irb(main):015:0> def hi(name)
irb(main):016:1> puts "Hello #{name}!"
irb(main):017:1> end
=> :hi
irb(main):018:0> hi("Matz")
Hello Matz!
=> nil

So it works… but let’s take a second to see what’s going on here.

Holding Spots in a String

What’s the #{name} bit? That’s Ruby’s way of inserting something into a string. The bit between the braces is turned into a string (if it isn’t one already) and then substituted into the outer string at that point. You can also use this to make sure that someone’s name is properly capitalized:

irb(main):019:0> def hi(name = "World")
irb(main):020:1> puts "Hello #{name.capitalize}!"
irb(main):021:1> end
=> :hi
irb(main):022:0> hi "chris"
Hello Chris!
=> nil
irb(main):023:0> hi
Hello World!
=> nil

A couple of other tricks to spot here. One is that we’re calling the method without parentheses again. If it’s obvious what you’re doing, the parentheses are optional. The other trick is the default parameter World. What this is saying is “If the name isn’t supplied, use the default name of "World"”.

Evolving Into a Greeter

What if we want a real greeter around, one that remembers your name and welcomes you and treats you always with respect. You might want to use an object for that. Let’s create a “Greeter” class.

irb(main):024:0> class Greeter
irb(main):025:1>   def initialize(name = "World")
irb(main):026:2>     @name = name
irb(main):027:2>   end
irb(main):028:1>   def say_hi
irb(main):029:2>     puts "Hi #{@name}!"
irb(main):030:2>   end
irb(main):031:1>   def say_bye
irb(main):032:2>     puts "Bye #{@name}, come back soon."
irb(main):033:2>   end
irb(main):034:1> end
=> :say_bye

The new keyword here is class. This defines a new class called Greeter and a bunch of methods for that class. Also notice @name. This is an instance variable, and is available to all the methods of the class. As you can see it’s used by say_hi and say_bye.

So how do we get this Greeter class set in motion? Create an object.

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