Methods

Declare a method

def method_name(parameter1, parameter2)
    puts "#{parameter1} #{parameter2}"
    parameter1 + parameter2
end

---

res = method_name(20, 10)
# output => 30
def method_name(parameter1, parameter2)
    puts "#{parameter1} #{parameter2}"
    return parameter1 + parameter2
end
# output => 30

Call method

res = method_name(parameter1, parameter2)
# Methods can be called without parentheses
res = method_name parameter1, parameter2

Class method

Class methods are class-level methods. There are multiple ways to define class methods

class Mobile
    def self.ring
        "ring ring ring..."
    end
end

Mobile.ring

---

class Mobile
    def Mobile.ring
        "ring ring ring..."
    end
end
Mobile.ring

---

class Mobile
    class << self
    def ring
        "ring ring ring..."
       end
    end
end
Mobile.ring

Class methods are instance methods of class objects. When a new class is created, an object of type "Class" is initialized and assigned to a global constant (in this case Mobile)

Mobile = Class.new do
    def self.ring
        "ring ring ring..."
    end
end
Mobile.ring

Mobile = Class.new
class << Mobile
    def ring
        "ring ring ring..."
    end
end
Mobile.ring

Use another parameter as default value

def method_name(num1, num2 = num1)
    return num1 + num2
end
res = method_name(10)
# output => 20

Define default values for method parameters

def method_name(parameter1, parameter2, type = "ADD")
    puts "#{parameter1} #{parameter2}"
    return parameter1 + parameter2 if type == "ADD"
    return parameter1 - parameter2 if type == "SUB"
end
res = method_name(20, 10)
# output => 30

Pass variable length arguments to method parameters

def method_name(type, *values)
    return values.reduce(:+) if type == "ADD"
    return values.reduce(:-) if type == "SUB"
end
numbers = [2, 2, 2, 3, 3, 3]
res = method_name("ADD", *numbers)
# output => 15
res = method_name("SUB", *numbers)
# output => -11
# Or you can provide a value like this
res = method_name("ADD", 2, 2, 2, 3, 3, 3)
# output => 15

Modify object

a = ["Drama", "Mystery", "Crime",
"Sci-fi", "Disaster", "Thriller"]
a.sort
puts a
# We did not modify the object
# Drama
# Mystery
# Crime
# Sci-fi
# Disaster
# Thriller
a.sort!
puts a
# Modify object
# Crime
# Disaster
# Drama
# Mystery
# Sci-fi
# Thriller

When you want to modify the object, use ! after the method

Boolean method

In ruby, methods ending with a question mark (?) are called boolean methods, which return true or false

"some text".nil?
# false
nil.nil?
# true

You can have your own boolean method

def is_vowel?(char)
    ['a','e','i','o','u'].include? char
end
is_vowel? 'a'
# true
is_vowel? 'b'
# false

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