Q:

Slim ignoring class & style on f.select field? 

I'm sure I'm being blind, can you spot something I've missed:
= f.select :region, options_for_select(YAML.load_file("#{Rails.root}/config/regions.yml").collect{|x| [x[1]['name'], x[0]]}), class: "form-control", style: 'display:none;'

Slim just ignores the class & style statements, but everything else looks fine.  What am I doing wrong? ( rails 4). 

A:

select(object, method, choices = nil, options = {}, html_options = {},
  &block) public

If you look into your code,
= f.select :region, options_for_select(YAML.load_file("#{Rails.root}/config/regions.yml").collect{|x| [x[1]['name'], x[0]]}), class: "form-control", style: 'display:none;'

class and style should be in a place of html_options = {} but currently they are in options = {}, so they are discarded. 
The below works
= f.select :region, options_for_select(YAML.load_file("#{Rails.root}/config/regions.yml").collect{|x‌​| [x[1]['name'], x[0]]}), {}, {class: "form-control", style: 'display:none;'}

