Gaurav Varma

Ruby 2.7 introduces pattern matching as an experimental feature — a powerful new control flow tool that brings deconstruction and deep matching to your Ruby code.

What is Pattern Matching?

Pattern matching allows you to match against the structure of objects (arrays, hashes, or custom types) and extract values inline. It uses the new case in syntax to provide clean and expressive matching logic.

Basic Example

1case [0, 1, 2]
2in [0, x, y]
3  puts "x = #{x}, y = #{y}"
4end

This pattern matches the array [0, 1, 2] and destructures it: x = 1, y = 2.

Matching Hashes and Object Types

You can use type guards with destructuring:

1case { name: "Alice", age: 30 }
2in { name: String => name, age: Integer => age }
3  puts "#{name} is #{age}"
4end

This matches the hash shape, confirms the types, and binds values.

Find Pattern Support

In Ruby 2.7 and beyond, you can match an element within a larger array using the splat (*) syntax:

1json = { name: "John", friends: [{ name: "Alex", age: 24 }, { name: "Don", age: 25 }] }
2
3case json
4in { name: "John", friends: [*, { name: "Alex", age: age }, *] }
5  puts "Alex is #{age}"
6end

This works even if the element appears in the middle of the array — thanks to the find pattern.

Complex Matching with Arrays

You can match parts of arrays with trailing or leading elements using the splat operator:

1case ["alpha", 1, "beta", "gamma", 2, "a", "b", "c", 3]
2in [*pre, String => x, String => y, *post]
3  p pre   # => ["alpha", 1]
4  p x     # => "beta"
5  p y     # => "gamma"
6  p post  # => [2, "a", "b", "c", 3]
7end

This elegantly extracts the first matching sequence of two strings while capturing what's before and after.

When to Use It

Pattern matching is great for:

Cleaning up deeply nested if/case chains
Extracting values from API responses
Handling structured JSON-like data

Caveats

Pattern matching is experimental in Ruby 2.7 — syntax and behavior may evolve
Only available via case in syntax (no standalone in blocks)
Not all Ruby types and structures support pattern matching natively yet

Resources

Summary

Pattern matching in Ruby 2.7 opens the door to cleaner, safer, and more expressive control flow — especially when dealing with structured data. While still evolving, it's a game-changing addition worth exploring in your apps and experiments.

Ruby 2.7 introduces pattern matching (experimental)