What is the -> (dash greater than) operator in Ruby/Rails [duplicate]

Question

I just ran across the following line of code in a Rails app:

scope :for_uid, ->(external_id) { where(external_id: external_id) }

What does the -> operator mean? It's kind of hard to Google.

Answer 1

This is syntactic sugar.

->(external_id) { where(external_id: external_id) }

is equal to:

lambda { |external_id| where(external_id: external_id) }

Answer 2

It's new lambda notation. This syntax was introduced in ruby 1.9, and is used to define unnamed functions.

In your example it is scope defined by unnamed function.