Are there “rules” for Ruby syntactic sugar?

Question

I\'m learning the basics of Ruby (just starting out), and I came across the Hash.[] method. It was introduced with

a = [\"foo\", 1, \"bar\", 2]
=> [\"foo\", 1         


        

Answer 1

Hash["a", "b", "c", "d"] is equivalent to Hash.[]("a", "b", "c", "d"). Almost everything in Ruby is a method call. 5 + 5 is equivalent to 5.+(5).

Given a = ["a", "b", "c", "d"] Hash[*a] is equivalent to Hash["a", "b", "c", "d"], which in turn is equivalent to Hash.[]("a", "b", "c", "d"). Similarly, foo(*a) is equivalent to foo("a", "b", "c", "d") This is called the explode operator, and allows sending an array to a method and have each item in the array count as one argument to the method, instead of sending the array to the method as the first argument.

---

To specifically answer your update, there's nothing special that lets you put *a inside the brackets. The brackets is just sugar for a normal method call. The only "special" thing here is that you can send *a to any method.