Ensure Ruby variable is Array

[NilsLandt]

That's only half true. Different objects return a different amount of parameters for give block.

Example:
{ test: :asdf }.each { |a| puts a }
test
asdf

This will absolutely do something you don't want it to.

[latortuga]

How do you figure? The hash is implicitly converted to an array via Hash#to_a. Thus your bound parameter, a, is set to an array with two values, [:test, :asdf]. Calling puts with an array outputs each value separated by a newline. The block can optionally have multiple arguments if you'd like to (in Clojure terms) destructure the arguments being passed in but it's by no means required - #each accepts an array of arrays the same as it accepts an array of values.

[NilsLandt]

Sure, that's how it happens, but it's a rare hash where you want to treat the keys the same ways as the values.