Is it possible to specify formatting options for to_yaml in ruby?

About the hash options: see http://yaml4r.sourceforge.net/doc/page/examples.htm

Ex. 24: Using to_yaml with an options Hash

puts [[ 'Crispin', 'Glover' ]].to_yaml( :Indent => 4, :UseHeader => true, :UseVersion => true )
# prints:
#   --- %YAML:1.0
#   -
#       - Crispin
#       - Glover

Ex. 25: Available symbols for an options Hash

Indent: The default indentation to use when emitting (defaults to 2)
Separator: The default separator to use between documents (defaults to '---')
SortKeys: Sort Hash keys when emitting? (defaults to false)
UseHeader: Display the YAML header when emitting? (defaults to false)
UseVersion: Display the YAML version when emitting? (defaults to false)
AnchorFormat: A formatting string for anchor IDs when emitting (defaults to 'id%03d')
ExplicitTypes: Use explicit types when emitting? (defaults to false)
BestWidth: The character width to use when folding text (defaults to 80)
UseFold: Force folding of text when emitting? (defaults to false)
UseBlock: Force all text to be literal when emitting? (defaults to false)
Encoding: Unicode format to encode with (defaults to :Utf8; requires Iconv)

Starting from Ruby 1.9 psych is used as a default YAML engine. It supports some attributes: http://ruby-doc.org/stdlib-2.1.0/libdoc/psych/rdoc/Psych/Handler/DumperOptions.html

So for me it works:

irb(main):001:0> require 'yaml'
=> true
irb(main):002:0> puts [{'a'=> 'b', 'c'=> 'd'}, {'e'=> 'f', 'g'=>'h'}].to_yaml(:indentation => 4)
---
-   a: b
    c: d
-   e: f
    g: h

Just another hack to specify the output style, but this one allows to customize it per specific object, instead of globally (e.g. for all arrays).

https://gist.github.com/jirutka/31b1a61162e41d5064fc

Simple example:

class Movie
  attr_accessor :genres, :actors

  # method called by psych to render YAML
  def encode_with(coder)
    # render array inline (flow style)
    coder['genres'] = StyledYAML.inline(genres) if genres
    # render in default style (block)
    coder['actors'] = actors if actors
  end
end

This ugly hack seems to do the trick...

class Array
  def to_yaml_style
    :inline
  end
end

Browsing through ruby's source, I can't find any options I could pass to achieve the same. Default options are described in the lib/yaml/constants.rb.