What is a shorter version of this?:
from = hash.fetch(:from) to = hash.fetch(:to) name = hash.fetch(:name) # etc Note the fetch, I want to raise an error if the key doesn't exist.
There must be shorter version of it, like:
from, to, name = hash.fetch(:from, :to, :name) # <-- imaginary won't work It is OK to use ActiveSupport if required.
Use Hash's values_at method:
from, to, name = hash.values_at(:from, :to, :name) This will return nil for any keys that don't exist in the hash.
fetch too.
raise MyException if hsh_values.include? nilRuby 2.3 finally introduces the fetch_values method for hashes that straightforwardly achieves this:
{a: 1, b: 2}.fetch_values(:a, :b) # => [1, 2] {a: 1, b: 2}.fetch_values(:a, :c) # => KeyError: key not found: :c 
hash = {from: :foo, to: :bar, name: :buz} [:from, :to, :name].map{|sym| hash.fetch(sym)} # => [:foo, :bar, :buz] [:frog, :to, :name].map{|sym| hash.fetch(sym)} # => KeyError my_array = {from: 'Jamaica', to: 'St. Martin'}.values_at(:from, :to, :name) my_array.keys.any? {|key| element.nil?} && raise || my_array This will raise an error like you requested
my_array = {from: 'Jamaica', to: 'St. Martin', name: 'George'}.values_at(:from, :to, :name) my_array.keys.any? {|key| element.nil?} && raise || my_array This will return the array.
But OP asked for failing on a missing key...
class MissingKeyError < StandardError end my_hash = {from: 'Jamaica', to: 'St. Martin', name: 'George'} my_array = my_hash.values_at(:from, :to, :name) my_hash.keys.to_a == [:from, :to, :name] or raise MissingKeyError my_hash = {from: 'Jamaica', to: 'St. Martin'} my_array = my_hash.values_at(:from, :to, :name) my_hash.keys.to_a == [:from, :to, :name] or raise MissingKeyError 
nil value.
keys.to_a == [:from, :to, :name] is incorrect. The order will matter here, but the Hash keys have no particular order it should be at least keys.to_a - [:from, :to, :name] == []. Overall, it's just more effort than it's worth.You could initialise your hash with a default value of KeyError object. This will return an instance of KeyError if the key you are trying to fetch is not present. All you need to do then is check its (value's) class and raise it if its a KeyError.
hash = Hash.new(KeyError.new("key not found")) Let's add some data to this hash
hash[:a], hash[:b], hash[:c] = "Foo", "Bar", nil Finally look at the values and raise an error if key not found
hash.values_at(:a,:b,:c,:d).each {|v| raise v if v.class == KeyError} This will raise an exception if and only if key is not present. It'll not complain in case you have a key with nil value.
The simplest thing I would go for would be
from, to, name = [:from, :to, :name].map {|key| hash.fetch(key)} Alternatively, if you want to use values_at, you can use a Hash with a default value block:
hash=Hash.new {|h, k| raise KeyError.new("key not found: #{k.inspect}") } # ... populate hash from, to, name = hash.values_at(:from, :to, :name) # raises KeyError on missing key Or, if you're so inclined, monkey-patch Hash
class ::Hash def fetch_all(*args) args.map {|key| fetch(key)} end end from, to, name = hash.fetch_all :from, :to, :name Pattern matching is an experimental feature in Ruby 2.7.
hash = { from: 'me', to: 'you', name: 'experimental ruby' } hash in { from:, to:, name: } See https://rubyreferences.github.io/rubyref/language/pattern-matching.html
I needed to have a hash being returned so I did a patch:
class Hash def multi_fetch(*keys) keys.map { |key| [key, fetch(key)] }.to_h end end 
from = hash.fetch(:from); to = hash.fetch(:to);... instead of usinghash[:from]?fetchinstead of[], there is sometimes a need for using a fetch version ofvalues_at.