array-vs-array-wrap.rb

def print_result(desc)
  result = yield
  puts "#{desc} class=#{result.class} inspect=#{result.inspect}"
rescue => e
  warn "#{desc} fail: #{e}"
end

def test(obj)
  puts "\n== #{obj.inspect} == "

  print_result("[*obj]          =>") { [*obj] }
  print_result("Array(obj)      =>") { Array(obj) }
  print_result("Array.wrap(obj) =>") { Array.wrap(obj) }
end

# trivial cases work the same:

[nil, true, false, 161, [1, 3, 1, 2], { :foo => :bar }].each(&method(:test))

# things become different with objects that implement implicit (to_ary) and/or
# explicit (to_a) coercions:

test(1..3)

# now, let's go crazy:

class Dummy
  def initialize(to_a:, to_ary:)
    @to_a   = to_a
    @to_ary = to_ary

    define_singleton_method(:to_a) { @to_a }     if @to_a
    define_singleton_method(:to_ary) { @to_ary } if @to_ary
  end

  class << self
    alias [] new
  end
end

test(Dummy[:to_a => [1, 6, 1],  :to_ary => [1, 3, 1, 2]])
test(Dummy[:to_a => "AFA",      :to_ary => [1, 3, 1, 2]])
test(Dummy[:to_a => [1, 6, 1],  :to_ary => "ACAB"])
test(Dummy[:to_a => [1, 6, 1],  :to_ary => nil])
test(Dummy[:to_a => nil,        :to_ary => [1, 6, 1]])
test(Dummy[:to_a => "AFA",      :to_ary => nil])
test(Dummy[:to_a => nil,        :to_ary => "AFA"])
test(Dummy[:to_a => nil,        :to_ary => nil])

Seems like Array.wrap is the most obvious implementation.

To make it easier to think of those methods, here's brief outline of behaviours:

Array(object)

• Return object as is if it's an Array
• Otherwise coerce object implicitly (if object responds to #to_ary)
  • Raise TypeError if coercion returned in non-Array
• Otherwise coerce object explicitly (if object responds to #to_a)
  • Raise TypeError if coercion returned non-Array
• Otherwise wrap object into an Array (as in: [object])

Array.wrap(object)

• Return object as is if it's an Array
• Otherwise coerce object implicitly (if object responds to #to_ary)
  • Return result of coercion as is if it's truthy (anything but nil or false)
• Otherwise wrap object into an Array (as in: [object])