Writing a custom YAML emitter

ruby-talk
1

Hi all,

I'm trying to understand how to write a custom YAML emitter. As fun and interesting as Why's documentation is, I don't quite get how to do what I need.

What I'm looking for is a way of avoiding emitting certain instance variables. Say I have a class like this:

class Book
   attr_accessor :title, :chapter_titles
   attr_accessor :current_page
end

When I save it, I want to save the permanent features like "title" and "chapter_titles", but I want to forget the current page.

I think the YAML representation would be something like:

--- !ruby/object:Bar
title: Fun with YAML
chapter_titles:
   - your first yaml document
   - daily yaml chores
   - advanced yaml fun

From looking at "rubytypes.rb", it looks like if I redefine "to_yaml_properties" to return ["@title", "@chapter_titles"] it should work. But is this the right way? Is there another preferred way?

Ben

2

Ben Giddings wrote:

From looking at "rubytypes.rb", it looks like if I redefine "to_yaml_properties" to return ["@title", "@chapter_titles"] it should work. But is this the right way? Is there another preferred way?

That's it. The to_yaml_properties is generally what I use 90% of the time.

If you decide you want to write a full-blown to_yaml method, I'd look at the to_yaml methods in rubytypes.rb to get an idea of how it's done, as the deep-down-to-the-black-black-sea-floor API isn't documentated at all.

_why