是否可以在 ruby 中为 to_yaml 指定格式选项？

Question

The code

require 'yaml'
puts YAML.load("
is_something:
  values: ['yes', 'no']
").to_yaml

produces

--- 
is_something: 
  values: 
  - "yes"
  - "no"

While this is a correct yaml, it just looks ugly when you have a hash of arrays. Is there a way for me to get to_yaml to produce the inline array version of the yaml?

An options hash can be passed to to_yaml but how do you use it?

Edit 0: Thanks Pozsár Balázs. But, as of ruby 1.8.7 (2009-04-08 patchlevel 160), the options hash does not work as advertised. :(

irb
irb(main):001:0> require 'yaml'
=> true
irb(main):002:0> puts [[ 'Crispin', 'Glover' ]].to_yaml( :Indent => 4, :UseHeader => true, :UseVersion => true )
--- 
- - Crispin
  - Glover
=> nil

Answer 1

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)

Answer 2

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

Answer 3

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 thelib/yaml/constants.rb .

Answer 4

Just another hack to specify the output style, but this one allows to customize it per specific object, instead of globally (eg 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

Answer 5

The latest versions of Ruby use the Psych module for YAML parsing. There aren't many options that you can pass but you can change indention and line width. Check the latest Psych documentation for more details.

Answer 6

Use Psych directly.

Indentation has no effect: my_yaml.to_yaml(:indentation => 2)

Indentation works: Psych.dump(my_yaml, :indentation => 8)