In Ruby what does "=>" mean and how does it work?

ruby-on-rails ruby operators symbols hashrocket
Dustin Martin picture Dustin Martin · Jan 11, 2011 · Viewed 32.2k times · Source

While learning Ruby I've come across the "=>" operator on occasion. Usually I see it in the form of 

:symbol => value

and it seems to be used frequently when passing values to functions. What exactly is that operator called? What does it do/mean? Is it built into Ruby or is it something that different frameworks like Rails and DataMapper add to the symbol class? Is it only used in conjunction with the symbol class? Thanks.

Answer

sepp2k picture sepp2k · Jan 11, 2011

=> separates the keys from the values in a hashmap literal. It is not overloadable and not specifically connected to symbols.

A hashmap literal has the form {key1 => value1, key2 => value2, ...}, but when used as the last parameter of a function, you can leave off the curly braces. So when you see a function call like f(:a => 1, :b => 2), f is called with one argument, which is a hashmap that has the keys :a and :b and the values 1 and 2.

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