til/ruby/use-rescue-as-part-of-inline-statement.md

Use Rescue As Part Of Inline Statement

In Ruby I typically think of rescue as block syntax that I can use to handle exceptions.

begin
  User.update!(password:)
rescue
  puts "There was an issue updating the password"
end

The rescue keyword can also be used as part of an inline statement as a way of providing a fallback value when the first part of the statement raises.

For instance, if I'm trying to access some value on an array that happens to be nil, it is going to raise:

> scores.first
(irb):7:in '<main>': undefined method 'first' for nil (NoMethodError)

I can instead tack on a rescue 0 which will give it 0 as a fallback value:

> scores.first rescue 0
=> 0

Of course, there are more idiomatic ways to handle this kind of situation in Ruby. Maybe something like this:

> Array(scores).first || 0
=> 0

Another way I've seen this inline rescue used is to print out the exception caused by that line of code, using $! (the global variable for the most recently raised exception).

> scores.first rescue puts $!
undefined method 'first' for nil
=> nil

That is a one-liner for the following:

begin
  scores.first
rescue => e
  puts e
end

The big caveat that goes with this is the same one that goes with any other blanket rescue block. If you are indiscriminately rescuing exceptions without being intentional about what you are rescuing and why, you could be potentially burying exceptions that you need to know about.