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 Arraw.wrap returns such a 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, though special-cases nil to return an empty array.

The last point is particularly worth comparing for some enumerables:

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

Array("foo\nbar")        # => ["foo\n", "bar"], in Ruby 1.8
Array.wrap("foo\nbar")   # => ["foo\nbar"]

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

[*object]

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

Thus, in this case the behavior is different for nil, and the differences with Kernel#Array explained above apply to the rest of +object+s.

# File activesupport/lib/active_support/core_ext/array/wrap.rb, line 39
  def self.wrap(object)
    if object.nil?
      []
    elsif object.respond_to?(:to_ary)
      object.to_ary
    else
      [object]
    end
  end