Coalesce

Do you write code like this? val = maybe_nil || fallback

If so, you are part of the problem!

false is a perfectly non-nil object, and you're excluding it out of convenience!

The null coalescing operator ?? is a C# idiom that provides a concise fallback mechanism for expressions that return null.

Object maybeObject = null;
Object fallbackObject = new Object();
Object obj = maybeObject ?? fallbackObject;

In Ruby, we generally write this:

maybe_object = nil
fallback_object = Object.new
obj = maybe_object || fallback_object

However, this idiom is only an approximation, and introduces subtle bugs when we try to allow false values:

maybe_val = false # assumed to be a valid value
fallback_val = 5
val = maybe_val || fallback_val # => 5, whoops!

With coalesce, you can write this instead:

maybe_val = false # assumed to be a valid value
fallback_val = 5
val = maybe_val._? fallback_val # => false, like we expected!

And if you still need the short-circuiting behavior of the || operator, you can pass a block instead:

val = maybe_val._? { generate_fallback(data) }

I've noticed a positive side-effect of using _? is that I explicitly call out when I'm counting on the short-circuiting behavior, and that awareness of the short-circuiting behavior is causing me to use it in ways I would never use ||.

For example, using it to assert an object's existence before returning it.

def give_me_the_data
  @data_finder.try_to_find_data._? { raise "Oh no, we suck at finding data!" }
end

I probably wouldn't think to use a || there, and it might look weird, especially with a more complex expression.

And, of course, I'm grateful to be reunited with my long lost friend, false.