From: Steve Howell <showell30@...>
Date: 2010-03-30T13:35:10+09:00
Subject: coercing nil/obj to false/true

I know this probably comes up a lot, but I could not Google the exact
question as I'm formulating it.

Is there a way to avoid this idiom?

def is_there_one(whatever)
  !some_call_to_lib_that_returns_object_or_nil(whatever).nil?
end

The above code tersely coerces a result to a boolean value, but it's
hard to read, because it's a double negative, and the "!" negative is
lexically separated from the "nil?" negative.

I occasionally do this instead:

 x = some_call_to_lib_that_returns_object_or_nil
 x.nil?

That's more readable for me, but more verbose, and I can never decide
what to name "x."

I can add something like this to my codebase, but I'm wondering if
something similar is already built in:

def to_boolean x
    return !x.nil?
end

def is_there_an_x_like(whatever)
  to_boolean(some_call_to_lib_x_that_returns_object_or_nil(whatever))
end

def is_there_a_y_like(whatever)
  to_boolean(some_call_to_y_lib_that_returns_object_or_nil(whatever))
end

Finally, I can just have my method return obj or nil, and let the
callers use it in boolean expressions, but my fear there is that I set
the wrong expectation for the caller, if I later return a different
object, when my intention is only to indicate whether a query succeeds
or not.  (You guessed it, this is motivated by ActiveRecord, but it's
really a Ruby question.)

Thoughts?