Why is the splat used inside an array definition here?

Question

def initialize(apps, catch=404)
  @apps = []; @has_app = {}
  apps.each { |app| add app }

  @catch = {}
  [*catch].each { |status| @catch[status] = true }
end
         


        

Answer 1

I think the best way to understand this is to look what is happening in irb.

So let's initialize an empty hash, @catch:

>> @catch = {}
=> {}
>> @catch.class
=> Hash

Now let's see what happens when the parameter catch goes to it's default value of 404:

>> catch=404
=> 404
>> [*catch].each { |status| @catch[status] = true }
=> [404]
>> @catch[404]
=> true

This gives us a better idea of what is going on. We can see that the splat operator is being used to build a Hash of responses. The response numbers are being used as a key and true is set as the value. So no matter how many items we have in catch, we can still build a Hash.

>> catch=[404, 301, 302, 303, 403]
=> [404, 301, 302, 303, 403]
>> [*catch].each { |status| @catch[status] = true }
=> [404, 301, 302, 303, 403]
>> @catch
=> {302=>true, 303=>true, 403=>true, 404=>true, 301=>true}

I hope this helps. Here is a link that helped me out a little bit:

http://theplana.wordpress.com/2007/03/03/ruby-idioms-the-splat-operator/