Process validation messages with Decorator

There was a terrible situation, and I wanted to process the validation message after it was generated according to the input pattern of the form, so make a note. For example, suppose you have the following form.

new.slim

= form_for post_form, url: confirm_post_path do |f|
  - if post_form.errors.present?
    ul
      - post_form.errors.full_messages.each do |msg| 
        li = msg

However, suppose that you have added the requirement to change the validation message if you choose a particular option in the form. In this case, errors.full_messages is an Array, so I checked the contents one by one with Decorator and replaced them with brute force.

new.slim

= form_for post_form, url: confirm_post_path do |f|
  - post_form_decorator = ::PostFormDecorator.new(f.object)
  - if post_form.errors.present?
    ul
      - post_form_decorator.post_error_display(post_form.errors.full_messages).each do |msg|
        li = msg

post_form_decorator.rb

class PostFormDecorator
  delegate_missing_to :@post_form

  def initialize(post_form)
    @post_form = post_form
  end

  def post_error_display(error_full_messages)
    error_full_messages.each do |msg|
      if @post_form.category == 'music'
        msg.gsub!(/#{@post_form.model.class.human_attribute_name(:author)}/, 'singer')
      end
    end
  end
end

Note that since the contents are replaced by a destructive method, it will not be replaced by gsub unless "!" Is added.