wrap

Wraps its argument in an array unless it is already an array (or array-like).

Specifically:

• If the argument is nil an empty list is returned.

• Otherwise, if the argument responds to to_ary it is invoked, and its result returned.

• Otherwise, returns an array with the argument as its single element.

  Array.wrap(nil)       # => []
  Array.wrap([1, 2, 3]) # => [1, 2, 3]
  Array.wrap(0)         # => [0]
  

This method is similar in purpose to Kernel#Array, but there are some differences:

• If the argument responds to to_ary the method is invoked. Kernel#Array moves on to try to_a if the returned value is nil, but Array.wrap returns nil right away.

• If the returned value from to_ary is neither nil nor an Array object, Kernel#Array raises an exception, while Array.wrap does not, it just returns the value.

• It does not call to_a on the argument, but returns an empty array if argument is nil.

The second point is easily explained with some enumerables:

Array(foo: :bar)      # => [[:foo, :bar]]
Array.wrap(foo: :bar) # => [{:foo=>:bar}]

There's also a related idiom that uses the splat operator:

[*object]

which returns [] for nil, but calls to Array(object) otherwise.

The differences with Kernel#Array explained above apply to the rest of objects.