[ruby-core:47074] [ruby-trunk - Feature #6840] YAML tag method

Issue #6840 has been updated by trans (Thomas Sawyer).


As I stated before, for my use case, I do *not* want users to use a support library. In fact, it's not just want, its a requirement. This format must be inter-operable. It doesn't mater if the user is programming in Perl, Python, Javascript or any other language. They need to be able to access the information just as readily. I'm not about to write a library for each possible language. The same holds for Ruby.

The "foo" type is a very specific YAML specification. If the user simply knows the name and version of the spec then they know what to expect. That's the most important thing. Any "Foo" library I write to support "foo" is just a convenience if it suites the purposes of the specifications user. But usually it will not, and should not. 

But this isn't really about my specific use case. There is a more fundamental issue here. Having to define a global handler upfront makes it impossible to handle the incoming information dynamically. It is one thing to make something difficult, it's another to make it impossible. I realize it sucks to add core methods, but in this case its really a feature that's needed.


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Feature #6840: YAML tag method
https://bugs.ruby-lang.org/issues/6840#change-28729

Author: trans (Thomas Sawyer)
Status: Rejected
Priority: Normal
Assignee: tenderlovemaking (Aaron Patterson)
Category: lib
Target version: 2.0.0


=begin
When loading YAML documents that have a tag, there doesn't seem to be anyway to query for that information.

  h = YAML.load("--- !foo\na: 1\nb: 2")
  h  #=> {"a"=>1, "b"=>2}
  h.what_method?  #=> "!foo"

I know about `YAML.add_domian_tag` and the like, but registering tags up front doesn't always fit the usecase. For instance, I am working on a project where I don't want the end users to have to use a support library to work with the data, and I certainly don't expect them to copy and paste dozens of lines of #add_domain_tag boilerplate to their projects. Yet the tags can be useful to them for type revison information, e.g.

  --- !foo/2

So this is the second revision of the foo type. The information could be important to consumer apps to ensure they handle the data properly.  

So I am proposing that Pysch add a method (maybe call it `#yaml_tag`), that can be used to get this information from an object when it has been loaded via YAML.
=end



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