gistfile1.txt

# if you define to_a
irb(main):001:0> class Foo
irb(main):002:1>   def to_a
irb(main):003:2>     puts "hi"
irb(main):004:2>     []
irb(main):005:2>   end
irb(main):006:1> end
=> nil
irb(main):007:0> [*Foo.new]
hi
=> []
irb(main):008:0> Array(Foo.new)
hi
=> []

# nil.to_a is []
irb(main):009:0> nil.to_a
=> []

# if you don't define to_a
irb(main):010:0> class Bar
irb(main):011:1> end
=> nil
irb(main):012:0> [*Bar.new]
=> [#<Bar:0x007fb7c99867e0>]
irb(main):013:0> Array(Bar.new)
=> [#<Bar:0x007fb7c9987988>]