Stop ignoring pattern matching!

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

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! Hi, I’m Tom, I work at Shopify

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“get the most out of Ruby”

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Pattern matching

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It was added to Ruby 2.7 in 2019

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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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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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Briefly: why bother?

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So why aren’t you using it?

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OK OK, what’s pattern matching?

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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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Recognising values & extracting their pieces Recognising values & extracting their pieces

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

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

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A completely separate syntax A completely separate syntax

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Patterns: the basic bits

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Value pattern

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Array pattern

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Hash pattern

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Alternative pattern

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Smash them all together!

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Idea: “case when” → “case in”

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Patterns: the intermediate bits

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Rest pattern

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Variable pattern

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Smash them all together!

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Real-world examples

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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) https://docs.ruby-lang.org/en/3.1/syntax/pattern_matching_rdoc.html

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Okay, that was a lot about pattern matching

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

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Gotchas

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Rails doesn’t embrace pattern matching yet

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

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Undefined behaviour

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e.g. variables in unmatched patterns

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“Experimental”…

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“Find patterns” are still experimental in Ruby 3.1

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…but Ruby moves on

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In summary then

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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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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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https://tomstu.art/stop-ignoring-pattern-matching Thanks!