In Ruby, if "global_variables.class" returns "Array", how do you tell whether global_variables is an array or a method?

Question

In Ruby, if global_variables.class returns Array, how do you tell whether global_variables is an array or a method?

Answer 1

Dig this:

>> global_variables
=> ["$-l", "$LOADED_FEATURES", "$?", ... , "$SAFE", "$!"]
>> method(:global_variables)
=> #<Method: Object(Kernel)#global_variables>

For comparison:

>> method(:foo)
NameError: undefined method `foo' for class `Object'
    from (irb):6:in `method'
    from (irb):6
>> 

Answer 2

Usually the global methods are defined by Kernel, which is an ancestor of Object. All methods written outside of a class are treated as private methods of Object.

irb(main):031:0> Object.private_methods.select{|x| x.to_s.start_with? 'gl'}
=> [:global_variables]

irb(main):032:0> f = [1,2,3]
=> [1, 2, 3]
irb(main):033:0> f.class
=> Array
irb(main):037:0> Object.private_methods.select{|x| x.to_s.start_with? 'f'}
=> [:format, :fail, :fork]

Answer 3

When Ruby sees a bareword, it always checks first if there is a local variable with that name. If there isn't, it tries to call a method:

>> def foo
..   "bar"
..   end
=> nil
>> foo = "lala"
=> "lala"
>> foo
=> "lala"
>> # to explicitly call the method
..   foo()
=> "bar"

If it can't resolve the name as either a local var or method, you get the following error:

>> bar
NameError: undefined local variable or method `bar' for #<Object:0x000001008b8e58>
    from (irb):1

Since you didn't assign to 'global_variables' before, it has to be a method.