Different parse priorities when argument is Hash

Question

Two cases:

ruby-1.9.2-p180 > puts {}.class

 => NilClass

and

ruby-1.9.2-p180 > puts "a".class
String
 => nil

It looks like puts {}.class is equivalent to (puts {}).class and puts "a".class is equivalent to puts ("a".class). Why is it so?

Answer 1

It's treating {} as a block, not as a hash. RubyInside says so, and also shows how you can prove it using Ripper.