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Importing Modules in Ruby: Understanding Include and Extend

Include and extend are two essential keywords in Ruby that are used to import modules into a program. Modules are chunks of code that contain classes, methods, and constants, which can be reused in various programs.

In programming, reusability is a critical factor, and modules offer the perfect solution for developers who want to reuse their code across different projects. However, to effectively use modules in Ruby, one must understand how to import them into the program using include and extend.

In this article, we explore the concept of include and extend, the limitations of calling methods in included and extended modules, and the solutions to these problems.

Include in Ruby

Include is a keyword in Ruby that is used to import modules into a program. When a module is included in a class, the code within the module becomes part of the class.

This allows the class to access the methods and constants within the module. For example, suppose we have a module called ‘Maths’ that has a method called ‘addition.’ We can include this module in a class called ‘Calculator’ as follows:

“`

module Maths

def addition(a, b)

a + b

end

end

class Calculator

include Maths

end

“`

In the code above, we have defined a module called ‘Maths,’ which has a single method called ‘addition.’ We then include this module in the ‘Calculator’ class using ‘include Maths.’ Once we include the module, the ‘addition’ method becomes part of the class definition. We can then create an instance of the ‘Calculator’ class and call the ‘addition’ method as shown below:

“`

calc = Calculator.new

calc.addition(2, 3) #=> 5

“`

Extend in Ruby

Extend is another keyword in Ruby used to import modules into a program. The difference between include and extend is that, when a module is extended, its methods become class methods as opposed to instance methods.

To better understand the difference, let us revise the example we used earlier, but this time, we will use extend instead of include. “`

module Maths

def addition(a, b)

a + b

end

end

class Calculator

extend Maths

end

“`

In the code above, we define a module called ‘Maths,’ which has a single method ‘addition.’ We then use the ‘extend Maths’ keyword to extend the module in the ‘Calculator’ class definition. Once we extend the module, we can call the ‘addition’ method directly on the class definition as shown below:

“`

Calculator.addition(2, 3) #=> 5

“`

The output is the same as we would expect when calling an instance method, but in this case, we are calling a class method.

Using Include and

Extend in Ruby

Using include and extend is simple in Ruby. Suppose we have a module called ‘Module1,’ and we want to include it in a class called ‘Class1.’ We would use the keyword include as follows:

“`

module Module1

def method1

puts “I am method1”

end

end

class Class1

include Module1

end

instance1 = Class1.new

instance1.method1 #=> outputs “I am method1”

“`

In the example above, we define a module ‘Module1’ that has a single method, ‘method1.’ We then include this module in the class definition of ‘Class1’ using ‘include Module1.’ Once we include the module, any instance of the class ‘Class1’ can call the ‘method1’ as an instance method. The ‘extend’ keyword works almost similarly to ‘include,’ only that the methods defined in the module become class methods, and we use the ‘.’ instead of the ‘#’ to call them:

“`

module Module1

def self.method1

puts “I am a class method”

end

end

class Class1

extend Module1

end

Class1.method1 #=> outputs “I am a class method”

“`

In this example, we define a module ‘Module1’ that has a class method ‘method1.’ We then extend the module in the class definition of ‘Class1’ using ‘extend Module1.’ Once we extend the module, we can call the ‘method1’ method directly on the class itself.

Limitations of calling Methods in included and extended modules

When working with modules in Ruby, one of the common issues that developers encounter is calling a method in a module that has been included or extended into another class. This becomes a problem when the method’s name clashes with another method either in the class or the module being called.

For example:

“`

module Module1

def method1

puts “I am method 1 from module1”

end

end

module Module2

include Module1

def method1

puts “I am method 1 from module2”

end

end

class Class1

include Module2

end

“`

In this example, we define two modules ‘Module1’ and ‘Module2.’ The ‘Module2’ module includes the ‘Module1’ module and has a method called ‘method1.’ We then create a class ‘Class1’ and include the ‘Module2’ module. The problem arises when we call the ‘method1’ on an instance of Class1:

“`

c1 = Class1.new

c1.method1 #=> outputs “I am method 1 from module2”

“`

The output is not what we anticipated because the ‘method1’ in ‘Module2’ overrides the ‘method1’ in ‘Module1.’ Therefore, when called, it executes the ‘method1’ in ‘Module2.’

Solution to the Issue

To avoid the error mentioned above, we can define methods as private in a module to stop them from being called directly from the class definition. “`

module Module1

def method1

puts “I am method 1 from module1”

end

end

module Module2

include Module1

private def method1

puts “I am method 1 from module2”

end

end

class Class1

include Module2

end

“`

In this example, we make the method ‘method1’ in ‘Module2’ private. Therefore, it can no longer be called directly from ‘Class1.’ Instead, ‘method1’ from ‘Module1’ is called if we call ‘method1’ on an instance of ‘Class1.’

“`

c1 = Class1.new

c1.method1 #=> outputs “I am method 1 from module2”

“`

In conclusion, include and extend are valuable keywords in Ruby that are used to import modules into a program.

While there may be limitations in calling methods in included and extended modules, they can be avoided by defining methods as private in the module. Understanding the differences between these keywords and the solutions to their limitations is critical to effective use of modules in Ruby.

The use of modules in Ruby is essential for reusability of code across various programs. The keywords include and extend are used to import modules into a program.

While calling methods in included and extended modules may cause issues, defining methods as private in the module can resolve the problem. The differences between include and extend and the solutions to their limitations are critical to effective use of modules in Ruby.

Understanding these concepts can help developers to write efficient and reusable codes, reducing coding time and increasing productivity.

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