Question

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Is there any difference between the :key => “value” and key: “value” hash notations?

What’s the difference between this:

method: :delete

and this?

:method => :delete

I’m guessing it has to do with different versions of Rails but not sure. I have only worked in Rails 3.x.

Answer 1

They are completely equivalent, except the first can only be used since ruby 1.9 (and higher, of course).

In ruby 1.8 the hash syntax used the =>, also known as the hash rocket. You could put anything in front, and anything behind, but the thing in front is your key, behind the value. If you have a symbol as key, and a symbol as value, you would write:

:method => :delete

But you could also write

{ 1 => 'one', :2 => 'two', 'THREE' => 3 }

Now, for ruby 1.9.x, a new shorter syntax was introduced. Since most people use symbols as keys, you can now write:

method: :delete

Which is just a shorter/cleaner version. Also note that it is possible to mix both styles, which in some cases is needed.

E.g. in ruby 1.8 you would write:

{ :class => 'smthg', :'data-type' => 'a type' }

This would translate to the following in ruby 1.9

{ class: 'smthg', :'data-type' => 'a type' }

Note that you can still keep using the “old” hash syntax as well. It is a matter of preference. Personally for hashes with only symbols as keys, I use the clean/short version. I generally try not to mix hash-style in a single hash 🙂