Immutability in Ruby

By Lorenzo Barasti

What do we mean with 'immutability'?

In object-oriented and functional programming, an immutable object is an object whose state cannot be modified after it is created

Wikipedia

What is it good for?

What is it good for?

• Testability
• Predictability
• Debugging

What is it good for?

• Testability

- factoring out time dependencies
- running tests concurrently
- avoiding afterAll, beforeAll

What is it good for?

• Parallelization comes more natural
• More emphasis on your data-flow
• Readability (?)
• Performance (??)

Scala Docs

Vector is a collection type [...] that addresses the inefficiency for random access on lists. Vectors allow accessing any element of the list in “effectively” constant time.

A real-world example from Scala

what about downsides?

what about downsides?

• Immutable and mutable data-structures don't play well together
• Integration with non-functional frameworks can be challenging
• When dealing with stateful functions extra care must be taken  

References

• An Introduction to immutability in Ruby by valve - probably the best place to start if you are new to the topic
• Immutability in Ruby - a very thorough article about the value of immutable data structures from Deveo's blog
• Immutable Ruby - a brilliant talk by Michael Fairley
• Hamster - a Ruby library that provides "Efficient, immutable, and thread-safe collection classes for Ruby"
• Scala Vector - documentation page
• To abstract or not to abstract? - interesting opinion about the value of abstraction vs efficiency by Mike Perham

THANK YOU for Listening!