Understanding The Ruby Next & Break Keywords

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Keywords, like next & break are part of the Ruby programming language, so if you want a complete understanding of Ruby you need to know how they work.

What are they used for?

Well, in Ruby, we have all kinds of loops.

Like:

  • while
  • until
  • each

When writing a loop, you may want to skip an iteration, or to end the loop early.

That’s where the next & break keywords come in!

Let’s find out how to use them.

Ruby Next Keyword (Skip Iteration)

The next keyword allows you to skip one iteration.

Example:

Let’s say you’re counting strings.

And for some reason you don’t want to count strings with a size of 4.

You could do this:

strings = ["one", "two", "four", "five"]

strings.inject(0) do |sum, str|
  next if str.size == 4

  sum + str.size
end

# nil

This code is NOT going to work.

You get nil.

Why?

Because next returns nil by default, just like calling return without a return value.

As you may know…

Using inject takes the last value returned by the block & that becomes the first argument of the next iteration.

In other words, sum becomes nil.

The solution?

Change the next line to this:

next sum if str.size == 4

This makes next return the value of sum.

If performance is not the highest priority (often it isn’t), you could pre-filter the array to avoid having to use next.

Or even better:

strings = ["one", "two", "four", "five"]

strings.inject(0) { |sum, str| str.size == 4 ? sum : sum + str.size }

# 6

This is a ternary operator.

I think Ruby gives you enough tools to avoid having to use next.

Use them!

Ruby Break Keyword (Exit Loop Early)

The break keyword is like next, but it ends the loop & returns a value, instead of skipping just one iteration.

It can be used for an early return from a loop.

Why not use the return keyword? Because it will exit from the current method, not just the loop.

Or to end an unconditional loop.

Like this:

count = 0

loop do
  break if count == 10

  puts count

  count += 1
end

This prints a list of numbers, from 0 to 9.

A better alternative would be to use the times method, the upto method, or a range plus the each method.

Example:

0.upto(9).each(&method(:puts))

This &method(:puts) is just a shortcut to call puts for each number.

Avoiding Confusion: Next As A Ruby Method

Just because something exists as a keyword, it doesn’t mean it can’t be used as a method name.

A few classes in Ruby implement next as a method.

Like String & Integer.

Example:

1.next
# 2

The result isn’t surprising, right?

How about this:

"zz".next
# "aaa"

That’s a bit more interesting!

How does this work?

Well, every class implements its version of next, which contains the logic for the next value.

For Integers, this is just +1.

For Strings, it increments the last character by one (next in alphabet / +1 for numbers), then if there’s a carryover (9 -> 0, z -> a), it will increment the next character on the left.

Summary

You’ve learned about the next & break keywords in Ruby, how they help you skip iterations, or stop a loop early.

Now it’s your turn to practice your Ruby skills 🙂

Thanks for reading!