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...

Transcript

1. Learning from other languages
   Immutability
   

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

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6. Mutability
   This is in contrast to a mutable object, which can be
   modified after it is created.
   

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7. Why is
   immutability
   good?
   

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8. Why is immutability good?
   → Inherently thread safe
   

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9. Why is immutability good?
   → Inherently thread safe
   → More memory efficient
   

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10. Why is immutability good?
    → Inherently thread safe
    → More memory efficient
    → No side effects
    

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11. Side effects?
    

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12. Side effects?
    In medicine, a side effect is an effect, whether
    therapeutic or adverse, that is secondary to the one
    intended;
    

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13. Side effects?
    In computer science a side effect is when a function
    or expression modifies some state outside its scope.
    

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14. Side effects?
    a = "string"
    def some_method(takes_a_string)
    takes_a_string.upcase!
    end
    some_method(a)
    

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15. Side effects?
    a = "string"
    def some_method(takes_a_string)
    takes_a_string.upcase!
    end
    some_method(a)
    puts a
    # => "STRING"
    

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16. Side effects?
    heros = {turtle: "Michaelenglo"}
    def mutate(hash)
    hash[:turtle] = "Rafael"
    end
    mutate heros
    # => "Rafael"
    heros
    # => {:turtle=>"Rafael"}
    

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17. Side effects?
    my.contacts << Person.new
    # => [#, #]
    

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19. Immutability in other languages
    Elixir - everything is immutable.
    

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20. Immutability in other languages
    Ada, C#, C++, Java, Perl, Python, JavaScript, Racket,
    Scala
    

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21. Immutability
    in Ruby
    

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22. Immutability in Ruby
    → Frozen objects
    

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23. Immutability in Ruby
    "my_string".freeze
    {a: :hash}.freeze
    any_object.freeze
    

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24. 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
    

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25. Immutability in Ruby
    → Frozen objects
    → Primitives such as numbers and symbols
    

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26. Immutability in Ruby
    6 += 2
    # SyntaxError: (irb):9: syntax error,
    # unexpected tOP_ASGN, expecting end-of-input
    

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27. Immutability in Ruby
    → Frozen objects
    → Primitives such as numbers and symbols
    → String literals from Ruby 2.3, optionally
    

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28. Frozen string
    ruby --enable-frozen-string-literal
    # frozen_string_literal: true
    

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29. Frozen string
    # frozen_string_literal: true
    "Hello".upcase!
    `upcase!': can't modify frozen String (RuntimeError)
    x = String.new('Hello')
    x.upcase!
    puts x #=> 'HELLO'
    

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30. Immutability in Ruby
    → Libararies such as:
    → ice_nine (deep freezing objects)
    → values immutable structs
    → immutable-ruby immutable enumerables
    

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31. Conclusion
    

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32. Conclusion - Benefits
    → Immutability helps with thread safety
    → Immutability can save memory usage
    → Immutability has the potential for cleaner, side
    effect free code.
    

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33. Conclusion - Drawbacks
    → In some cases mutability is more performant (e.g.
    RSpec mutates strings to avoid allocations)
    

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34. Thanks
    @jonrowe
    

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