Ruby: Clean code for checking nil /false conditional statement?

Question

I always meet this Ruby problem, I want to write it more cleanly.

var a can be nil
a.value can also be nil
a.value has possible true or false value

if (not a.nil?) && (not a.value.nil?) && a.value == false
  puts "a value is not available"
else
  puts "a value is true"
end

The problem is that the conditional statement is too clumsy and hard to read. How can I improve the checking nil and false conditional statement?

Thanks, I am a Ruby newbie

Answer 1

Ruby on rails has an extension called try which allows you to write:

 if a.try(:value) == false

which is very clean. Without try, you can just write

 if a && a.value == false

If a.value is nil, it is not false, so that is ok :)

If it is possible that a.value is not defined (which would raise an exception), I would write that as follows:

if a && a.respond_to?(:value) && a.value == false

[UPDATE: after ruby 2.3]

Since ruby 2.3 there is an even shorter version:

if a&.value == false

which is almost equivalent to a.try(:value) (but is pure ruby). Differences:

• if value does not exist, the &. operator will throw, try will just return nil (preferable or not?)(note: try! would also throw).
• when cascading try or &. they also handle false differently. This follows logically from previous difference, try will return nil, while &. will throw because false knows no methods :P