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Methods

A method in Ruby is a set of expressions that returns a value. Within a method, you can organize your code into subroutines which can be easily invoked from other areas of their program.

A method name must start a letter or a character with the eight-bit set. It may contain letters, numbers, an _ (underscore or low line) or a character with the eight-bit set. The convention is to use underscores to separate words in a multiword method name:

  • A method definition starts with the 'def' keyword followed by the method name.
  • Method parameters are specified between parentheses following the method name.
  • The method definition ends with 'end' keyword on the bottom.

Example :

def print_data(value)
  puts value 
end

Method Names

A method name must start a letter or a character with the eight-bit set. It may contain letters, numbers, an _ (underscore or low line) or a character with the eight-bit set. The convention is to use underscores to separate words in a multiword method name.

  • Method names are US-ASCII compatible since the keys to type them exist on all keyboards.
  • Method names may end with a ! (bang or exclamation mark), a ? (question mark) or = equals sign.
  • The bang methods(! at the end of method name) are called and executed just like any other method.
  • Methods that end with a question mark by convention return boolean. But they may not always return just true or false, often they return an object to indicate a true value.
  • Methods that end with an equals sign indicate an assignment method. For assignment methods the return value is ignored, the arguments are returned instead.

Return Values:

By default, a method returns the last statement that was evaluated in the body of the method. You can do so by using the return keyword. In the following example, the last expression evaluated was the simple sum 100 + 200.

def add_values
  return 100 + 200
end

The statement is also used to return before the last expression is evaluated

def add_values
  return 100 + 200
end
  300 + 200  # this expression is never evaluated
end

For assignment methods, the return value is always ignored. Instead the argument will be returned:

def x = (value)
  return 100 + value
end

p(x = 500) # prints 500

Arguments

In Ruby a method can accept arguments.

  • The argument list follows the method name.
  • The parentheses around the arguments are optional.
  • Multiple arguments are separated by a comma.
  • The arguments are positional.

See the following example :

def add_values(num1, num2)
  return num1 + num2
end

In the above example when you call the method you must provide two arguments. Within the method body, the arguments are local variables. The method will then add two arguments and return the value. If given 100 and 200 this method will return 300.

Default Values

You can set default values of arguments. The default value does not need to appear first, but arguments with defaults must be grouped together.

def add_values(num1, num2 = 15)
  num1 + num2
end

Call a method

You can call methods with or without parentheses. Here is the syntax :

# With parentheses
UserMethod()

# Without parentheses
UserMethod

Here is an example :

# Without parentheses
def Print_String()
 puts("Method without parentheses")
end

# With parentheses
def Add_values(num1, num2)
  return num1 + num2
end

# Default Values
def default_values(num1, num2 = 12)
  return num1 + num2
end

Print_String()
puts(Add_values(100, 200))
puts(default_values(50))

Output :

Method without parentheses
300
62

Scope

You can define an instance method on a specific class with the class keyword :

class Student
  def admission
    # ...
  end
end

A method may be defined on another object. You may define a "class method" like this:

class Student
  def self.admission
    # ...
  end
end

Here is the syntax for adding a method to an object :

language = "Ruby"

def language.tutorial
 puts(self + ", Learning.")
end

language.tutorial # returns "Ruby, Learning."

Note: self is a keyword referring to the current object under consideration by the compiler.

Overriding

When Ruby executes the def keyword, it simply redefines it (whether the method already exists or not). This is called overriding. See the following example :

def language
 puts("We are learning PHP")
end

def language
 puts("We are learning Ruby")
end

# Now call the method
language

Output :

We are learning Ruby

More on Arguments

Array Decomposition:

You can extract values from an Array using extra parentheses in the arguments:

def add_numbers((n1, n2))
  p n1: n1, n2: n2
end

add_numbers([10, 20]))

Output:

{:n1=>10, :n2=>20}

Extra argument in the array is ignored :

def add_numbers((n1, n2))
  p n1: n1, n2: n2
end

add_numbers([10, 20, 30]))

Output:

{:n1=>10, :n2=>20}

Using a * you can collect the remaining arguments. This splits an Array into a first element and the rest:

def add_numbers((n1, *n2))
  p n1: n1, n2: n2
end

add_numbers([10, 20, 30]))

Output:

{:n1=>10, :n2=>[20, 30]}

Array/Hash Argument:

Prefix an argument with * to convert an argument to an Array. The array argument must be the last positional argument, it must appear before any keyword arguments.

def gather_arguments(*arguments)
  p arguments
end
gather_arguments 1, 2, 3 # prints [1, 2, 3]

The array argument will capture a Hash as the last entry if a hash was sent by the caller after all positional arguments. This only occurs if the method does not declare any keyword arguments.

gather_arguments 1, a: 2 # prints [1, {:a=>2}]

Also, note that a bare * can be used to ignore arguments:

def ignore_arguments(*)
end

Keyword Arguments:

Keyword arguments are similar to positional arguments with default values:

def add_values(first: 1, second: 2)
  first + second
end

Arbitrary keyword arguments will be accepted with **:

def gather_arguments(first: nil, **rest)
  p first, rest
end

gather_arguments first: 1, second: 2, third: 3
# prints 1 then {:second=>2, :third=>3}

Note :
a. When calling a method with keyword arguments the arguments may appear in any order. If an unknown keyword argument is sent by the caller an ArgumentError is raised.
b. When mixing keyword arguments and positional arguments, all positional arguments must appear before any keyword arguments.

Block Argument:

The block argument is used to pass a block to another method. The block argument is indicated by & and must come last.

def each_item(&block)
  @items.each(&block)
end

Exception Handling:

Methods have an implied exception handling block so you do not need to use begin or end to handle exceptions.

def my_method
  begin
    # code that may raise an exception
  rescue
    # handle exception
  end
end

May be written as:

def my_method
  # code that may raise an exception
rescue
  # handle exception
end

If you wish to rescue an exception for only part of your method use begin and end. For more details see the page on exception handling



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