Ruby - what does Array.any?(&:nil?) mean?

Question

I am new to ruby and working through a tutorial but am not sure what this line of code means:

[movie, version_number].any?(&:nil?)

From my research, Array.any? returns true if any of the elements of the array are not false or nil. And &:nil? means to call to_proc() on the symbol :nil? i.e. :nil?.to_proc so the statement is equivalent to

[movie, version_number].any?(:nil?.to_proc)

which is equivalent to

[movie, version_number].any?{|item| item.nil?}

Further, any? Passes each element of the collection (in this case, Array) to the {|item| item.nil?} block.

When you put them together, does the line of code mean, call nil? on each element in the Array before calling .any? on the array, i.e. is it equivalent to:

[movie.nil?, version_number.nil?].any?

Or, in plain English, are any of movie or version_number equivalent to nil?

Answer 1

From Symbol#to_proc documentation:

Returns a Proc object which respond to the given method by sym.

(1..3).collect(&:to_s)  #=> ["1", "2", "3"] 

So in your case this is effectively the same as writing:

[movie, version_number].any?{|item| item.nil? }

any? expects a block^[1] to be passed, which will be evaluated for each item, and will return true if the block evaluates to true for any of the members.

The to_proc method on Symbol is basically a convenience shortcut, when you just want to call a single method on the item passed to the block. As in the example above, this leads to shorter code than explicitly defining the block.

^[1] Refer this article on blocks, procs and lambdas in ruby