I’ve been working on a custom form builder that adds several convenient 
features to select(); together, they make it easier to select from a collection 
of ActiveRecords. Basically, instead of doing this:


  f.select(:folder_id, @folders.map { |folder| [folder.name, folder.id] }, 
disabled: @folders.select(&:deleted?).map(&:id))


You can do this:


  f.select(:folder_id, @folders, record_label: :name, disabled: :deleted?)


With these changes, the disabled option can now take a proc or symbol that 
filters the available choices; the record_label option tells select() that the 
choices are ActiveRecord objects and how to get the “name” for each one.


I’ve pasted my current implementation below—it’s not ready to be dropped into 
ActionView (it should be factored differently, could probably be written 
better, and it doesn’t support grouped options), but it should give you an idea 
of what I have in mind.


Is this something people might be interested in incorporating into Rails? If 
so, I can start turning this into a workable patch; if not, I needn’t bother.


  def select(method, choices, options = {}, html_options = {})
    # If disabled option is a Symbol, Method, or Proc, build a 
    # disabled list by filtering the choices list with it.
    options[:disabled] = choices.select(&options[:disabled]) if 
options[:disabled].respond_to? :to_proc
    
    # The record_label option is a shorthand for:
    #   choice_template: [record_label, :id]
    if label = options.delete(:record_label)
      options[:choice_template] = [label, :id]
    end
    
    # If choice_template option is present, run all the choices through it.
    if template = options.delete(:choice_template)
      template = make_array(template).map(&:to_proc)
      choices = choices.map { |choice| template.map { |t| t.(choice) } }
      
      # If :disabled is present, run its contents through the same template 
(well, the last 
      # item in the template, which controls the value).
      options[:disabled] = make_array(options[:disabled]).map(&template.last)
    end
    
    # Call into super
    super(method, choices, options, html_options)
  end
  
private
  def make_array(obj)
    Array.try_convert(obj) || [obj]
  end


—
Brent Royal-Gordon
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