Question

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What is the -> (stab) operator in Ruby?

I am trying to learn Objects on Rails book and find problem to understand what -> operator mean.

The code is:

describe Blog do
   subject       { Blog.new(->{entries}) }
   let(:entries) { [] }

   it "has no entries" do
     subject.entries.must_be_empty
   end

   describe "#new_entry" do
     let(:new_post) { OpenStruct.new }

   before do
     subject.post_source = ->{ new_post }
   end

   it "returns a new post" do
     subject.new_post.must_equal new_post
   end
end

I spend a lot of time to find it in any docs, but couldn’t

Answer 1

That’s a new syntax for lambda. You can also write it like this:

subject.post_source = lambda { new_post }

Here’s how old and new versions look like with parameters (thanks to Michael Kohl for suggestion):

v_old = lambda {|a, b| a + b}
v_new = ->(a, b) { a + b}

v_old.call(1, 2) # => 3
v_new.call(3, 4) # => 7