Find the Last Matching Element with rfind

Instead of…

…reversing the array or using reverse_each to find from the end:

numbers = [2, 2, 3, 4, 6, 7, 8]

numbers.reverse.find(&:odd?)
#=> 7

# or
numbers.reverse_each.find(&:even?)
#=> 8

Use…

…Ruby 4.0’s rfind method:

numbers = [2, 2, 3, 4, 6, 7, 8]

numbers.rfind(&:odd?)
#=> 7

# with a block
numbers.rfind { it.even? }
#=> 8

Why?

The rfind method iterates backwards from the last element, returning the first element that matches the given condition. It’s the reverse of find, which starts from the beginning.

This is more efficient than reverse.find or reverse_each.find because it doesn’t create an intermediate reversed array or enumerator in memory. For large arrays, this can make a noticeable difference.

You might wonder why this was added to Array specifically rather than Enumerable. The Enumerable module relies on the #each method, which only works in the forward direction. The only way to scan backwards generically would be to convert to an array first, defeating the purpose. However, arrays can be traversed in either direction efficiently by the nature of their implementation in the Ruby VM.

Why not?

If you’re not yet on Ruby 4.0, you’ll need to stick with reverse_each.find for now. It’s not a dramatic difference, but rfind is cleaner and more intentional.

For very small arrays, the performance difference is negligible, so the main benefit is readability—your intent is clearer when you use rfind.

Did you know?

In the same changeset, Kevin Newton also added a specific implementation of Array#find (and its alias #detect) rather than relying on the Enumerable version. This is a performance improvement for arrays.