Ruby: Object.to_a replacement

Question

I need to convert a passed in argument (single object or collection) to an Array. I don\'t know what the argument is. If it is an Array already, I want to leave it, otherwis

Answer 1

Wow, someone just necromanced a really old thread. :-O But since I don't see it included yet, I'll add one more way for completeness' sake:

arg = [*arg]

This will splat the argument if it already is an array (thus removing one level of nesting) or create a one-argument array otherwise:

arg = [1,2,3]
[*arg] #=> [1, 2, 3]
arg = 1
[*arg] #=> [1]

Answer 2

Use the method Kernel#Array:

Array([1,2,3]) #=> [1, 2, 3]
Array(123) #=> [123]

Yes it may look like a class at first but this is actually a method that starts with a capital letter.

Answer 3

You can take the duck typing aproach if that suits the problem better, make a list of all the methods you need, and check if the object already have them, if not, make it an array:

[:[], :each, :etc...].all? { |m| obj.respond_to? m } ? obj : [obj]

The advantage is that you give the object a chance to implement it's own semantics for indexed access.

Answer 4

I do this a lot, and always use:

arg = [arg] unless arg.is_a?(Array)

Though if you know you're never passing in arrays as individual arguments you can also do:

arg = [arg].flatten

Answer 5

I'm not sure if this helps, but what I often need is not that the arg be an array, but that the arg responds to each.

arg = [arg] unless arg.respond_to? :each

Answer 6

It seems only Object.to_a is deprecated, removing a default to_a and forcing each class to define its own (e.g., Hash.to_a).

self.to_a       #=> -:1: warning: default `to_a' will be obsolete
"hello".to_a    #=> ["hello"]
Time.new.to_a   #=> [39, 54, 8, 9, 4, 2003, 3, 99, true, "CDT"]

h = { "c" => 300, "a" => 100, "d" => 400, "c" => 300  }
h.to_a   #=> [["a", 100], ["c", 300], ["d", 400]]

If your argument is an instance of Object, try:

Hash.new(obj).to_a

---

@Daniel [comment to Ollivier]: The point is that I don't know what the argument is. If it is an array already, I want to leave it, otherwise create a one-element array.

If that's the case, try:

obj = [obj] if !obj.is_a?(Array)