From: Joel VanderWerf <vjoel@...>
Date: 2004-03-15T06:19:41+09:00
Subject: yaml and ruby symbols

Since today is apparently the first day of the new YAML year, or at 
least a major event on the YAML calendar, here's something else I've 
been wondering about.

I tend to prefer symbols to strings as hash keys (for immutability and 
efficiency reasons), but I'm not crazy about how they look in YAML:

   irb> y({:foo=>1})
   ---
   !ruby/sym foo: 1

whereas string keys look more natural:

   irb> y({"foo"=>1})
   ---
   foo: 1

Yet it seems that YAML.load is quite capable of recognizing a nice, 
natural format for symbols:

   irb> s="---\n:foo: 1\n"
   irb> puts s
   ---
   :foo: 1
   irb> YAML.load(s)
   => {:foo=>1}

And this notation is not ambiguous with strings that happen to begin 
with a colon:

   irb> y({":foo"=>1})
   ---
   ":foo": 1

Is it possible for Symbol#to_yaml to take an option that will dump 
symbols in this simpler way? (You'd lose some portability, I guess, so 
maybe the option should not be on by default.)

This is the implementation I tried, but apparently I don't understand 
how the opts argument of #to_yaml gets propagated (or why it doesn't).

require 'yaml'

class Symbol
    def to_yaml( opts = {} )
       YAML::quick_emit( nil, opts ) { |out|
          out << (opts[:simple_symbols] ? ":" : "!ruby/sym ")
          self.id2name.to_yaml( :Emitter => out )
       }
    end
end

foo_yaml = :foo.to_yaml({:simple_symbols => true})
puts foo_yaml
# ==>
# --- :foo
#
# Good so far!

foo = YAML.load(foo_yaml)
p foo
# ==>
# :foo
#
# Still good.

h = {:foo=>1}

puts h.to_yaml
# ==>
# ---
# !ruby/sym foo: 1
#
# Expected.

puts h.to_yaml({:simple_symbols => true})
# ==>
# ---
# !ruby/sym foo: 1
#
# Expected:
# ---
# :foo: 1