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Stop ignoring pattern matching!

Stop ignoring pattern matching!

Pattern matching was introduced as a major language feature in Ruby 2.7 and has been improved in subsequent releases, but not many people are using it yet. It’s really helpful and can make your programs clearer, simpler, safer, or all three. So why aren’t you using it? You should totally use it! I’ll show you how.

Given at Brighton Ruby 2022. A video is available at https://tomstu.art/stop-ignoring-pattern-matching.

Tom Stuart

June 30, 2022

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  1. Tom Stuart, Brighton Ruby 2022
    Stop ignoring pattern matching!
    It’s really good!

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  2. ! Hi, I’m Tom, I work at Shopify

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  3. “get the most out of Ruby”

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  4. Pattern matching

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  5. It was added to Ruby 2.7 in 2019

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  7. It’s really helpful and it can make
    your code clearer, simpler & safer
    It’s really helpful and it can make
    your code clearer, simpler & safer

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  8. Here is what I am about to say
    Not including this slide, that would take forever
    • Briefly: why bother?

    • OK OK, what’s pattern matching?

    • The basic bits

    • The intermediate bits

    • The advanced bits

    • Gotchas

    • The end

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  9. Briefly: why bother?

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  21. So why aren’t you using it?

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  22. OK OK, what’s pattern matching?

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  23. https://docs.ruby-lang.org/en/3.1/syntax/pattern_matching_rdoc.html
    “Pattern matching is a feature allowing
    deep matching of structured values:
    checking the structure and binding the
    matched parts to local variables.”

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  24. Recognising values &
    extracting their pieces
    Recognising values &
    extracting their pieces

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  25. expression in pattern # returns true or false
    expression => pattern # succeeds or raises
    as of Ruby 3.1.2

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  26. case expression
    in pattern
    # …
    in pattern
    # …
    in pattern
    # …
    end # succeeds or raises
    as of Ruby 3.1.2

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  27. A completely separate syntax
    A completely separate syntax

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  28. Patterns: the basic bits

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  29. Value pattern

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  32. Array pattern

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  34. Hash pattern

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  36. Alternative pattern

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  38. Smash them all together!

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  40. Idea: “case when” → “case in”

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  45. Patterns: the intermediate bits

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  46. Rest pattern

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  48. Variable pattern

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  52. Smash them all together!

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  54. Real-world examples

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  58. Patterns: the advanced bits
    Please read the documentation, it’s good actually
    • Guard clauses
    • Variable and expression pinning
    • Array pattern coercion (#deconstruct)
    • Hash pattern coercion (#deconstruct_keys)

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  59. Okay, that was a lot
    about pattern matching

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  60. (Maybe this is why
    you’re not using it?)

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  61. Gotchas

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  62. Rails doesn’t embrace
    pattern matching yet

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  63. (Maybe this is why
    you’re not using it?)

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  70. Undefined behaviour

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  71. e.g. variables in
    unmatched patterns

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  74. “Experimental”…

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  78. “Find patterns” are
    still experimental in Ruby 3.1

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  81. …but Ruby moves on

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  82. In summary then

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  83. In summary then
    Big picture ideas you can remember
    • Ruby has pattern matching now
    • …and has done for years
    • it can make your code clearer, simpler and safer
    • …so it’s a huge shame to ignore it!
    • don’t be afraid of new Ruby features, and don’t shy away from trying stuff
    even if you don’t see other people doing it — someone has to go first

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  84. In summary then
    Concrete things you can actually do
    • try converting “case when” to “case in” to get some easy benefits
    • look for opportunities to match the entire shapes of arrays and hashes instead
    of checking their elements individually
    • once you’re comfortable, dip a toe into more advanced features (guards,
    variable pinning, #deconstruct & #deconstruct_keys, find patterns) to
    get more power out of pattern matching
    • write a conference talk or a blog post and spread the word

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  85. https://tomstu.art/stop-ignoring-pattern-matching

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