dash symbol

In the example below, what is the dash doing between the class
attribute and array:

(field_helpers -
[:label, :check_box, :radio_button, :fields_for, :hidden_field, :file_field]).each
do |selector|

In ruby a minus on an array removes elements. So its removing elements from the array.

Look at http://www.ruby-doc.org/core-1.9.3/Array.html#method-i-2D

Yeah so I would like to see the returned array of instance methods of
field_helpers of FormBuilder. I try to return it in console:

1.9.3p0 :016 > FormBuilder.field_helpers
NoMethodError: undefined method `field_helpers' for FormBuilder:Class

Why is it saying undefined method field_helpers when that method
exists on the FormBuilder class:

class_attribute :field_helpers

ok this was oversight on my part. First of all, instead of using the
helper helper in the console, you can directly access actionview just
by specifying the constant. So
ActionView::Helpers::FormBuilder.instance_methods would work. But what
was oversight is that I was wondering that FormBuilder's field_helpers
class method which returns an array of methods for the object was
actually removing all the methods it defines. But if you look at its
assignment, it is grabbing the methods of FormHelper, not FormBuilder.
It does "FormHelper.instance_methods" and FormHelper is what defines
the key methods that we often invoke on the form builder that have
generic output:

[:convert_to_model, :form_for, :fields_for, :label, :text_field, :password_field, :hidden_field, :file_field, :text_area, :check_box, :radio_button, :search_field, :telephone_field, :phone_field, :url_field, :email_field, :number_field, :range_field]

The reason why we
exclude :label, :check_box, :radio_button, :fields_for, :hidden_field, :file_field
is because they have their own unqiue definition which is done in the
form builder itself.

So whene we cal text_field, for example, that method was dybamically
built using class_eval. and what it does is just call the method from
selector.inspect on tempalte, and of course the tempalte is
ActionView::Helpers::FormHelper, since that is also where form_for
itself is defined. and in our view we invoke form_for, where self is
ActionView with tha tmodule included.