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Functional Programming in Ruby: A Guide

Alessio Bussolari
2 min readDec 12, 2023


Functional programming (FP) is a paradigm that treats computation as the evaluation of mathematical functions and avoids changing-state and mutable data. While Ruby is primarily an object-oriented language, it also offers several features that make functional programming possible and effective.

Key Concepts of Functional Programming

  1. Immutability: Avoiding changing the state of objects after they are created.
  2. First-Class and Higher-Order Functions: Treating functions as first-class citizens and using functions as arguments or return values.
  3. Pure Functions: Functions that have no side effects and return a value that depends only on their input.
  4. Function Composition: Building complex operations out of simpler functions.

Implementing Functional Programming in Ruby

  • Leveraging Lambdas and Procs:
    In Ruby, lambdas and procs are first-class functions that can be stored in variables, passed as arguments, or returned from other functions.
adder = ->(x, y) { x + y }, 3) # => 5
  • Using Immutable Data Structures:
    While Ruby doesn’t enforce immutability, you can adopt a functional style by avoiding mutation of objects.



Alessio Bussolari

Ruby on Rails programmer since 2009. Current CTO at COSMIC SRL, where I lead the team in creating innovative solutions.