Ruby methods are very similar to functions in any other programming language. Ruby methods are used to bundle one or more repeatable statements into a single unit.

Method names should begin with a lowercase letter. If you begin a method name with an uppercase letter, Ruby might think that it is a constant and hence can parse the call incorrectly.

Methods should be defined before calling them, otherwise Ruby will raise an exception for undefined method invoking.

Syntax

def method_name [( [arg [= default]]...[, * arg [, &expr ]])]
   expr..
end

So, you can define a simple method as follows 

def method_name 
   expr..
end

You can represent a method that accepts parameters like this −

def method_name (var1, var2)
   expr..
end

You can set default values for the parameters, which will be used if method is called without passing the required parameters 

def method_name (var1 = value1, var2 = value2)
   expr..
end

Whenever you call the simple method, you write only the method name as follows 

method_name

However, when you call a method with parameters, you write the method name along with the parameters, such as −

method_name 25, 30

The most important drawback to using methods with parameters is that you need to remember the number of parameters whenever you call such methods. For example, if a method accepts three parameters and you pass only two, then Ruby displays an error.

Example

#!/usr/bin/ruby

def test(a1 = "Ruby", a2 = "Perl")
   puts "The programming language is #{a1}"
   puts "The programming language is #{a2}"
end
test "C", "C++"
test

This will produce the following result 

The programming language is C
The programming language is C++
The programming language is Ruby
The programming language is Perl

Return Values from Methods

Every method in Ruby returns a value by default. This returned value will be the value of the last statement. For example −

def test
   i = 100
   j = 10
   k = 0
end

This method, when called, will return the last declared variable k.

Ruby return Statement

The return statement in ruby is used to return one or more values from a Ruby Method.

Syntax

return [expr[`,' expr...]

If more than two expressions are given, the array containing these values will be the return value. If no expression given, nil will be the return value.

Example

return

OR

return 12

OR

return 1,2,3

Have a look at this example 

#!/usr/bin/ruby

def test
   i = 100
   j = 200
   k = 300
return i, j, k
end
var = test
puts var

Output

100
 200
 300

Variable Number of Parameters

Suppose you declare a method that takes two parameters, whenever you call this method, you need to pass two parameters along with it.

However, Ruby allows you to declare methods that work with a variable number of parameters. Let us examine a sample of this −

#!/usr/bin/ruby

def sample (*test)
   puts "The number of parameters is #{test.length}"
   for i in 0...test.length
      puts "The parameters are #{test[i]}"
   end
end
sample "Zara", "6", "F"
sample "Mac", "36", "M", "MCA"

In this code, you have declared a method sample that accepts one parameter test. However, this parameter is a variable parameter. This means that this parameter can take in any number of variables. So, the above code will produce the following result 

The number of parameters is 3
The parameters are Zara
The parameters are 6
The parameters are F
The number of parameters is 4
The parameters are Mac
The parameters are 36
The parameters are M

Class Methods

When a method is defined outside of the class definition, the method is marked as private by default. On the other hand, the methods defined in the class definition are marked as public by default. The default visibility and the private mark of the methods can be changed by public or private of the Module.

Whenever you want to access a method of a class, you first need to instantiate the class. Then, using the object, you can access any member of the class.

Ruby gives you a way to access a method without instantiating a class. Let us see how a class method is declared and accessed −

class Accounts
   def reading_charge
   end
   def Accounts.return_date
   end
end

See how the method return_date is declared. It is declared with the class name followed by a period, which is followed by the name of the method. You can access this class method directly as follows −

Accounts.return_date

To access this method, you need not create objects of the class Accounts.

Ruby alias Statement

This gives alias to methods or global variables. Aliases cannot be defined within the method body. The alias of the method keeps the current definition of the method, even when methods are overridden.

Making aliases for the numbered global variables ($1, $2,...) is prohibited. Overriding the built-in global variables may cause serious problems.

Syntax

alias method-name method-name 
alias global-variable-name global-variable-name

Example

alias foo bar 
alias $MATCH $&

Here we have defined foo alias for bar, and $MATCH is an alias for $&

Ruby undef Statement

This cancels the method definition. An undef cannot appear in the method body.

By using undef and alias, the interface of the class can be modified independently from the superclass, but notice it may be broke programs by the internal method call to self.

Syntax

undef method-name

Example

To undefine a method called bar do the following 

undef bar