What does -> mean in Ruby


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It is a lambda literal. Check this example:

 > plus_one = ->(x){x+1}
 => #<Proc:0x9fbaa00@(irb):3 (lambda)> 
 > plus_one.call(3)
 => 4 

A lambda literal is a constructor for Proc. A Proc is a way to have a block of code assigned to a variable. After this, you can call your block of code again, with different arguments, as many times as you wish.

This is how you can pass a "function" as parameter in ruby. In many languages, you could pass a reference to a function. In ruby, you can pass a Proc object.

In Ruby 1.9 you can use the stab operator -> to create a lambda.

l1 = lambda { puts "I'm a lambda" }
l2 = -> { puts "I'm a lambda" } 

The operator also accept arguments.

l1 = lambda(name) { puts "I'm a #{name}" }
l2 = ->(name) { puts "I'm a #{name}" } 

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