Fat is where dig meets fetch

The name is an acronym for "find at". It helps you avoid that nasty undefined method [] for nil when looking for values in a hash.

Say you have the following hash

hash = {
  "foo" => {
    "bar" => {
      "baz" => :value
    }
  }
}

To get your :value you usually do hash["foo"]["bar"]["baz"]. But what happens if "bar" doesn't exist? Yeap, BOOM! You will get an undefined method [] for nil error.

Using Fat you can walk the hash up to the :value (just like dig), but it'll raise an exception if it finds nil (just like fetch) at any point.

require "fat"

Fat.at(hash, "foo", "bar", "baz")
# => :value

Fat.at(hash, "foo", "not", "here")
# => Fat::FatError: foo.not is nil

Fat.at(hash, "foo", "bar", "nope")
# => Fat::FatError: foo.bar.nope is nil

You can specify a default return value with the default: keyword if you don't want an exception raised.

require "fat"

Fat.at(hash, "foo", "not", "here", default: "whoops")
# => "whoops"

If you set default: nil this method behaves exactly like Hash#dig, available from Ruby 2.3.0.

It's the same with Symbols

hash = {
  "foo" => {
    :bar => {
      "baz" => :value
    }
  }
}

Fat.at(hash, "foo", :bar, "baz")
# => :value

If you prefer to call hash.at you only need to include Fat into Hash.

Hash.include(Fat)

hash.at("foo", "bar", "baz")
# => :value

$ gem install fat