Methods in Ruby

Methods are used to don't repeat the same thing all along the program.

Creating Methods

To create a method use this syntax:

def my_first_method
  "Hello"
end

puts my_first_method  #=> "Hello"

Parameters and Arguments

Parameters are placeholder variables in the template of your method, whereas arguments are the actual variables that get passed to the method when it is called.

def add_ten(number)
  number + 10
end

puts add_ten(20)  #=> "30"

In this example, number is a parameter and 20 is an argument.

Default Parameters

If you don't want to always give parameters when calling a method, use default parameters:

def add_ten(number = 1)
  number + 10
end

puts add_ten(20)  #=> "30"
puts add_ten      #=> "11"

What Methods Return

Ruby offers implicit return for methods, it always returns the last expression that was evaluated.

And Ruby offers explicit return too, it is useful to write methods that check for input errors before continuing.

def even_odd(number)
  unless number.is_a? Numeric
    return "A number was not entered."
  end

  if number % 2 == 0
    "That is an even number."
  else
    "That is an odd number."
  end
end

puts even_odd(30) #=>  That is an even number.
puts even_odd("Egg") #=>  A number was not entered.

Predicate Methods

Methods that have a question mark (?) at the end of their name, such as even?, odd?, or between? are predicate methods, which is a naming convention that Ruby uses for methods that return a Boolean.

puts 3.even?  #=> false
puts 10.even?  #=> true
puts 171.odd?  #=> true

puts 13.between?(10, 15)  #=> true

Bang Methods

Methods that are denoted with an exclamation mark (!) at the end of the method name.

By adding a ! to the end of your method, you indicate that this method performs its action and simultaneously overwrites the value of the original object with the result.

whisper = "HEY"
puts whisper.downcase! #=> "hey"
puts whisper #=> "hey"