What do the square brackets mean here?

Question

I saw a line in a Rails app like this:

Order::PAYMENT_TYPES.map {|p| [t('.payment_type.'+p), p]}

PAYMENT_TYPE is a string array, and the letter t is used for i18n in Rails.

I'm not sure how the square brackets are used here. Apparently they are not for arrays or methods. And I will rewrite this to just {|p| t('.payment_type.'+p) } {|p| t('.payment_type.'+p) } .

So what's the Ruby grammar in this example?

Answer 1

Apparently they are not for arrays or methods

Well, it is an array literal

[t('.payment_type.'+p), p]
# ^ first element       ^ second

I will rewrite this to just ...

If this will work for you, go ahead. We don't know your app's specifics.

Answer 2

Ruby returns the last statement from a method or a block. In this case, with the brackets, the block returns an array of two items, so calling that block in map , if PAYMENT_TYPES had three items, would result in something like [ [a1, b1], [a2, b2], [a3, b3] ] .

Answer 3

You are correct that square brackets are not just used for arrays, you can also call Procs.

proc = lambda { |name| "Hello, #{name}" }
proc.call('Bob')
=> "Hello, Bob"

proc = lambda { |name| "Hello, #{name}" }
proc['Bob']
=> "Hello, Bob"

But in this case, as others have indicated, a new array is being returned resulting in a nested array of arrays.