Forum: Ruby why "Range" not worked on "to_ary" ?

>> (1..9).to_a
=> [1, 2, 3, 4, 5, 6, 7, 8, 9]
>> (1..9).to_ary
NoMethodError: undefined method `to_ary' for 1..9:Range
  from (irb):2
  from /usr/bin/irb:12:in `<main>'
>>

In the below code why "Range" not worked on "to_ary" ?

Try looking at the methods available to a Range.

$ irb
irb(main):001:0> a = (1..9)
=> 1..9
irb(main):002:0> a.public_methods.sort
=> ["==", "===", "=~", "__id__", "__send__", "all?", "any?", "begin",
"class", "clone", "collect", "count", "cycle", "detect", "display", 
"drop",
"drop_while", "dup", "each", "each_cons", "each_slice", 
"each_with_index",
"end", "entries", "enum_cons", "enum_for", "enum_slice", 
"enum_with_index",
"eql?", "equal?", "exclude_end?", "extend", "find", "find_all",
"find_index", "first", "freeze", "frozen?", "grep", "group_by", "hash",
"id", "include?", "inject", "inspect", "instance_eval", "instance_exec",
"instance_of?", "instance_variable_defined?", "instance_variable_get",
"instance_variable_set", "instance_variables", "is_a?", "kind_of?", 
"last",
"map", "max", "max_by", "member?", "method", "methods", "min", "min_by",
"minmax", "minmax_by", "nil?", "none?", "object_id", "one?", 
"partition",
"private_methods", "protected_methods", "public_methods", "reduce",
"reject", "respond_to?", "reverse_each", "select", "send",
"singleton_methods", "sort", "sort_by", "step", "taguri", "taguri=",
"taint", "tainted?", "take", "take_while", "tap", "to_a", "to_enum",
"to_s", "to_yaml", "to_yaml_properties", "to_yaml_style", "type",
"untaint", "zip"]

And there we have it to_a

yes,you are right. Now I have one thing to say that-

Array#try_convert(obj) : If obj is not already an array, attempts to 
convert it to one by calling its 'to_ary' method.

I have no handy example for that method here to paste,thus couldn't. 
Question is why then such implementation?

I don't think ranges can act as arrays that way, it is not guaranteed
that they are finite.

On Sat, Feb 23, 2013 at 2:35 PM, Xavier R. <lists@ruby-forum.com> wrote:
> yes,you are right. Now I have one thing to say that-
>
> Array#try_convert(obj) : If obj is not already an array, attempts to
> convert it to one by calling its 'to_ary' method.
>
> I have no handy example for that method here to paste,thus couldn't.
> Question is why then such implementation?

#to_ary is used to convert things that are fundamentally array-like,
i.e. they can be used in places (usually standard library methods)
where arrays can be used. A range is not fundamentally like an array,
because it doesn't consist of a finite number of elements (or really
any "elements" at all unless you want to count the endpoints). #to_a
is used to convert things in a way that's dictated by convention,
rather than a way that's inherent to the data themselves.