Psych::Nodes - ri - phpman

= Psych::Nodes

(from gem psych-5.4.0)
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= Overview

When using Psych.load to deserialize a YAML document, the document is
translated to an intermediary AST.  That intermediary AST is then
translated in to a Ruby object graph.

In the opposite direction, when using Psych.dump, the Ruby object graph
is translated to an intermediary AST which is then converted to a YAML
document.

Psych::Nodes contains all of the classes that make up the nodes of a
YAML AST.  You can manually build an AST and use one of the visitors
(see Psych::Visitors) to convert that AST to either a YAML document or
to a Ruby object graph.

Here is an example of building an AST that represents a list with one
scalar:

  # Create our nodes
  stream = Psych::Nodes::Stream.new
  doc    = Psych::Nodes::Document.new
  seq    = Psych::Nodes::Sequence.new
  scalar = Psych::Nodes::Scalar.new('foo')

  # Build up our tree
  stream.children << doc
  doc.children    << seq
  seq.children    << scalar

The stream is the root of the tree.  We can then convert the tree to
YAML:

  stream.to_yaml => "---\n- foo\n"

Or convert it to Ruby:

  stream.to_ruby => [["foo"]]

== YAML AST Requirements

A valid YAML AST must have one Psych::Nodes::Stream at the root.
 A Psych::Nodes::Stream node must have 1 or more Psych::Nodes::Document
nodes as children.

Psych::Nodes::Document nodes must have one and only one child.
That child may be one of:

* Psych::Nodes::Sequence
* Psych::Nodes::Mapping
* Psych::Nodes::Scalar

Psych::Nodes::Sequence and Psych::Nodes::Mapping nodes may have many
children, but Psych::Nodes::Mapping nodes should have an even number of
children.

All of these are valid children for Psych::Nodes::Sequence and
Psych::Nodes::Mapping nodes:

* Psych::Nodes::Sequence
* Psych::Nodes::Mapping
* Psych::Nodes::Scalar
* Psych::Nodes::Alias

Psych::Nodes::Scalar and Psych::Nodes::Alias are both terminal nodes and
should not have any children.







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