Creating an array containing a hash

Question

QUESTION EDIT - Breakdown how the 2nd example creates a hash.

I can't figure out why the first example below does not create a hash and the second one does.

a: :b
# => SyntaxError: (irb):1: syntax error, unexpected ':', expecting end-of-input

vs.

[a: :b]
# => [{:a => :b}]

Answer 1

When you just have a: :b that is a statement and it is invalid Ruby syntax.

When you have [a: :b], you are actually calling a method. The method you are calling is [](a: :b). When you give a: :b as the argument to a method Ruby sees it as a hash and gives the method {:a => :b} as it's argument. So the end result is the [{:a => :b}] that you are seeing.