[ruby-core:29376] Re: [Bug #3112] require "yaml" doesn't use psych as default

First of all, people want compatibility.
Although Ruby sometimes breaks compatibility, it is important.
We should keep compability until it has enough reason.

> Yes!  Many of these methods are exposing implementation specific details
> for syck.  For example, the "detect_implicit" method detects whether a
> YAML string is an implicit or explicit string.  "try_implicit" which
> attempts to use "detect_implicit".  "object_maker" calls allocate on
> a class and sets instance variables based on a hash.  These are clearly
> methods which should never be exposed as a public API.

An API is implementation specific is not enough reason.
Implementation can return some value as if it works.
YAML.detect_implicit seems such one.

If an API is depend on syck implementation and hard to emulate,
such API can be removed.
It will trouble some users and it is sorry, but it is unavoidable.

> Other methods are deprecated because they are simply duplicates.  For
> example, YAML.load_documents and YAML.each_document do _exactly_ the same thing.
> YAML.each_node and YAML.parse_documents do _exactly_ the same thing.

Duplication is not enough reason to break compatibility.

Yes, your preference should be respect.
You can remove them with some migrating process.

Usual Ruby's process of removing API is:
* mark the API as deprecated
* release some versions
* remove it

> On top of that, most of these methods are untested, which makes writing
> 100% compatible software impossible.  All of these methods could
> be added to Psych, but it wouldn't be guaranteed that they work the same
> way as Syck.

Of course 100% is impossible.
What we need is almost compatible.
"almost" means what people use.

> I understood from [ruby-core:28749], that Psych didn't need to have full
> compatibility.  The best way I could think to warn users and maintain
> compatibility is to default to the old parser and let users choose to
> use the new one.

If psych doesn't have enough compatibility to replace in 1.9.2,
we need some migration path.

> I am happy to add most of these to Psych, *if* Psych is going to be the
> default parser.  I do not want to support these methods long term
> though.  Please give me a clear direction, and I will make it happen.

If psych has enough compatibility, it can be a default parser in 1.9.2.
As far as I know, YAML.quick_emit breaks some applications like RubyGems.

Yeah, what is "enough compatibility" is the problem.
I think, Rails and its dependency can run can be a test.

-- 
NARUSE, Yui
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