Upgrade to Pro — share decks privately, control downloads, hide ads and more …

Learning From Other Languages - Immutability

Jon Rowe
March 13, 2018

Learning From Other Languages - Immutability

So many talks are about learning new languages and technology, but what can we bring back from those into Ruby...

Jon Rowe

March 13, 2018

More Decks by Jon Rowe

Other Decks in Technology


  1. Immutability In object-oriented and functional programming, an immutable object is

    an object whose state cannot be modified after it is created.
  2. Mutability This is in contrast to a mutable object, which

    can be modified after it is created.
  3. Side effects? In medicine, a side effect is an effect,

    whether therapeutic or adverse, that is secondary to the one intended;
  4. Side effects? In computer science a side effect is when

    a function or expression modifies some state outside its scope.
  5. Side effects? heros = {turtle: "Michaelenglo"} def mutate(hash) hash[:turtle] =

    "Rafael" end mutate heros # => "Rafael" heros # => {:turtle=>"Rafael"}
  6. Immutability in Ruby mutate("my_string".freeze) # => RuntimeError: can't modify frozen

    String {a: :hash}.freeze # => RuntimeError: can't modify frozen Hash any_object.freeze # => RuntimeError: can't modify frozen <Object>
  7. Immutability in Ruby 6 += 2 # SyntaxError: (irb):9: syntax

    error, # unexpected tOP_ASGN, expecting end-of-input
  8. Immutability in Ruby → Frozen objects → Primitives such as

    numbers and symbols → String literals from Ruby 2.3, optionally
  9. Frozen string # frozen_string_literal: true "Hello".upcase! `upcase!': can't modify frozen

    String (RuntimeError) x = String.new('Hello') x.upcase! puts x #=> 'HELLO'
  10. Immutability in Ruby → Libararies such as: → ice_nine (deep

    freezing objects) → values immutable structs → immutable-ruby immutable enumerables
  11. Conclusion - Benefits → Immutability helps with thread safety →

    Immutability can save memory usage → Immutability has the potential for cleaner, side effect free code.
  12. Conclusion - Drawbacks → In some cases mutability is more

    performant (e.g. RSpec mutates strings to avoid allocations)