Ruby Academy · Lesson

Find Patterns and Guards

Conditions in matches.

Lesson 3 of 413 steps

Find Patterns and Guards is a free Ruby Academy lesson on CoddyKit. This is lesson 3 of 4. Any 3 lessons of this learning path are free to read in full — after that, CoddyKit PRO unlocks every lesson, plus hands-on practice with a built-in code editor and a 24/7 AI tutor. It is part of the Ruby Academy learning path, and your progress syncs across the web and the CoddyKit app. The Ruby Academy course includes 4 lessons in total.

Guard Conditions

Add an if or unless guard to a pattern. The branch matches only when both the pattern and the condition succeed.

case 7
in Integer => n if n.odd?
  puts 'odd integer'
end

Guards Use Bound Variables

The guard can reference variables bound by the pattern, so you can express rich conditions about the matched data.

case [4, 9]
in [a, b] if a < b
  puts 'ascending pair'
end

unless Guards

An unless guard matches when the condition is false, the inverse of if.

case 0
in Integer => n unless n.positive?
  puts 'zero or negative'
end

Multiple Guarded Branches

Combine guards across branches to build a clear decision ladder.

def grade(score)
  case score
  in Integer => s if s >= 90 then 'A'
  in Integer => s if s >= 70 then 'B'
  else 'C'
  end
end
puts(grade(85))

Find Patterns

A find pattern [*, x, *] searches an array for a sub-pattern anywhere inside it, with splats on both ends.

case [1, 2, 3, 4]
in [*, 3, *]
  puts 'contains a 3'
end

Binding Inside a Find

The matched element in a find pattern can be bound, capturing the found value.

case [10, 20, 30]
in [*, x, *] if x > 25
  puts("found #{x}")
end

Capturing Surroundings

Both splats in a find pattern can be named to capture the elements before and after the match.

case [1, 2, 99, 4, 5]
in [*before, 99, *after]
  p before
  p after
end

Find a Typed Element

Find patterns combine with type patterns to locate the first element of a given type.

case [1, 'hi', 2]
in [*, String => word, *]
  puts(word)
end

Guards vs Patterns

Express what you can structurally in the pattern, and use guards only for conditions patterns cannot capture (like numeric comparisons or method calls).

case { role: 'admin', age: 40 }
in { role: 'admin', age: } if age >= 18
  puts 'adult admin'
end

Combining Find and Guard

Find patterns and guards together let you ask: does any element satisfy this condition?

numbers = [3, 5, 8, 11]
case numbers
in [*, n, *] if n.even?
  puts("first even-ish hit: #{n}")
end

Order of Branches

Branches are tried top to bottom; the first match wins. Put more specific guarded patterns before general ones.

case 100
in Integer => n if n > 50 then puts 'big'
in Integer then puts 'small'
end

Quick Check

What does the find pattern [*, x, *] do?

Answer it in the interactive lesson

Recap: Find Patterns and Guards

You added conditions and search to matching:

Guards if / unless refine a pattern
Guards can use bound variables
Find patterns [*, x, *] search anywhere
Both splats can be named to capture surroundings
First matching branch wins, so order matters

case [1, 7, 3]
in [*, x, *] if x > 5 then puts x
end

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Frequently Asked Questions

Is the “Find Patterns and Guards” lesson free?

Yes — any 3 lessons of the Ruby Academy learning path, including “Find Patterns and Guards”, are free to read in full here on the web. After that, CoddyKit PRO unlocks every lesson, plus interactive practice with a built-in code editor and a 24/7 AI tutor. The Ruby Academy course includes 4 lessons in total.

What will I learn in “Find Patterns and Guards”?

Conditions in matches. You practise Ruby Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Ruby Academy?

No prior experience is required. Ruby Academy on CoddyKit is structured for beginners through advanced learners, so you can start here or from the beginning and move at your own pace. This is lesson 3 of 4.

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