Re: Documentation for Psych in Ruby 1.9.3?

On Oct 19, 2012, at 07:52 , [e-mail] wrote:

> I'm searching and searching... but I can not find the
> documentation for Psych on <http://www.ruby-doc.org/stdlib-1.9.3/>.
> 
> If I am not mistaken it practically replaces YAML and is part
> of the standard library.

`ri Psych` works great. See below. That said, you shouldn't be using Psych directly. Use YAML instead:

% ri19 YAML
= YAML

(from ruby core)
------------------------------------------------------------------------------
The YAML module allows you to use one of the two YAML engines that ship with
ruby.  By default Psych is used but the old and unmaintained Syck may be
chosen.

See Psych or Syck for usage and documentation.

To set the YAML engine to syck:

  YAML::ENGINE.yamler = 'syck'

To set the YAML engine back to psych:

  YAML::ENGINE.yamler = 'psych'
...

% ri19 Psych

= Psych

(from ruby core)
------------------------------------------------------------------------------
This exists just to satify bugs in marshal'd gemspecs that contain a reference
to YAML::PrivateType. We prune these out in Specification._load, but if we
don't have the constant, Marshal blows up.

This exists just to satify bugs in marshal'd gemspecs that contain a reference
to YAML::PrivateType. We prune these out in Specification._load, but if we
don't have the constant, Marshal blows up.

= Overview

Psych is a YAML parser and emitter.  Psych leverages
libyaml[http://libyaml.org] for it's YAML parsing and emitting capabilities.
In addition to wrapping libyaml, Psych also knows how to serialize and
de-serialize most Ruby objects to and from the YAML format.

= I NEED TO PARSE OR EMIT YAML RIGHT NOW!

  # Parse some YAML
  Psych.load("--- foo") # => "foo"

  # Emit some YAML
  Psych.dump("foo")     # => "--- foo\n...\n"
  { :a => 'b'}.to_yaml  # => "---\n:a: b\n"

Got more time on your hands?  Keep on reading!

== YAML Parsing

Psych provides a range of interfaces for parsing a YAML document ranging from
low level to high level, depending on your parsing needs.  At the lowest
level, is an event based parser.  Mid level is access to the raw YAML AST, and
at the highest level is the ability to unmarshal YAML to ruby objects.

=== Low level parsing

The lowest level parser should be used when the YAML input is already known,
and the developer does not want to pay the price of building an AST or
automatic detection and conversion to ruby objects.  See Psych::Parser for
more information on using the event based parser.

=== Mid level parsing

Psych provides access to an AST produced from parsing a YAML document.  This
tree is built using the Psych::Parser and Psych::TreeBuilder.  The AST can be
examined and manipulated freely.  Please see Psych::parse_stream,
Psych::Nodes, and Psych::Nodes::Node for more information on dealing with YAML
syntax trees.

=== High level parsing

The high level YAML parser provided by Psych simply takes YAML as input and
returns a Ruby data structure.  For information on using the high level parser
see Psych.load

== YAML Emitting

Psych provides a range of interfaces ranging from low to high level for
producing YAML documents.  Very similar to the YAML parsing interfaces, Psych
provides at the lowest level, an event based system, mid-level is building a
YAML AST, and the highest level is converting a Ruby object straight to a YAML
document.

=== Low level emitting

The lowest level emitter is an event based system.  Events are sent to a
Psych::Emitter object.  That object knows how to convert the events to a YAML
document.  This interface should be used when document format is known in
advance or speed is a concern.  See Psych::Emitter for more information.

=== Mid level emitting

At the mid level is building an AST.  This AST is exactly the same as the AST
used when parsing a YAML document.  Users can build an AST by hand and the AST
knows how to emit itself as a YAML document.  See Psych::Nodes,
Psych::Nodes::Node, and Psych::TreeBuilder for more information on building a
YAML AST.

=== High level emitting

The high level emitter has the easiest interface.  Psych simply takes a Ruby
data structure and converts it to a YAML document.  See Psych.dump for more
information on dumping a Ruby data structure.
------------------------------------------------------------------------------
= Constants:

DEPRECATED:
  [not documented]

ENGINE:
  [not documented]

LIBYAML_VERSION:
  The version of libyaml Psych is using

VERSION:
  The version is Psych you're using


= Class methods:

  add_private_type
  add_ruby_type
  detect_implicit
  dump
  dump_stream
  libyaml_version
  load
  load_documents
  load_file
  load_stream
  object_maker
  parse
  parse_file
  parse_stream
  parser
  quick_emit
  read_type_class
  tagurize
  to_json