# YAML issue with Set?

**URL:** <https://www.ruby-forum.com/t/yaml-issue-with-set/87509>\
**Category:** Ruby\
**Created:** [March 3, 2007, 5:31am UTC](https://www.ruby-forum.com/t/yaml-issue-with-set/87509 "2007-03-03T05:31:11Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![thebox](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/91b2a8/32.png) [@thebox](https://www.ruby-forum.com/u/thebox)\
**Post date:** [March 3, 2007, 5:31am UTC](https://www.ruby-forum.com/t/yaml-issue-with-set/87509/1 "2007-03-03T05:31:11Z")

</div>

What am I doing wrong?

#!/opt/local/bin/ruby  
###############################  
require ‘set’  
require ‘yaml’  
require ‘tempfile’

def tempname(basename)  
file = Tempfile.new(basename)  
file.close(false)  
file.path  
end

class U  
attr\_accessor :name  
def initialize(n)  
@name = n  
end  
def ==(other)  
name == other.name  
end  
end

set = Set.new  
set.add(U.new(“one”))  
set.add(U.new(“two”))

filename = tempname(“set\_yaml”)  
File.open(filename, “w”) {|f| YAML.dump(set, f)}

another\_set = YAML.load(File.open(filename))

puts “#{set == another\_set}”  
###############################

The result that I get is the following:

###############################  
xxx:~ piergiulianobossi$ ./set\_yaml.rb  
/opt/local/lib/ruby/1.8/yaml.rb:133:in `load': syntax error on line 3, col -1:` name: one (ArgumentError)  
: true

!ruby/object:U ?  
name: two  
: true

’ from /opt/local/lib/ruby/1.8/yaml.rb:133:in `load’  
from ./set\_yaml.rb:30  
###############################

Running ruby on Mac OS/X 10.4

###############################  
xxx:~ piergiulianobossi$ ruby -v  
ruby 1.8.5 (2006-08-25) [i686-darwin8.8.1]  
###############################

---

<div class="post-metadata">

**Author:** ![thebox](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/91b2a8/32.png) [@thebox](https://www.ruby-forum.com/u/thebox)\
**Post date:** [March 3, 2007, 5:09pm UTC](https://www.ruby-forum.com/t/yaml-issue-with-set/87509/2 "2007-03-03T17:09:13Z")

</div>

Alle sabato 3 marzo 2007, thebox ha scritto:

> What am I doing wrong?  
> As far as I can tell (I’m not a YAML expert), no. I’ve made a few  
> trials, and  
> it seems that class Hash (which is used internally by Set), has problems  
> with  
> loading / dumping when keys are custom classes. For instance, using irb  
> (ruby -v gives ruby 1.8.5 (2006-12-25 patchlevel 12) [i686-linux], on  
> gentoo)  
> :

> > require ‘yaml’  
> > =\> true  
> > class C  
> > end  
> > =\> nil  
> > c=C.new  
> > =\> #\<C:0xb78bd5b4\>  
> > h={c=\>‘test’}  
> > =\> {#\<C:0xb78bd5b4\>=\>“test”}  
> > str=YAML.dump h  
> > =\> “— \n!ruby/object:C ? {}\n: test\n\n”  
> > h1=YAML.load str  
> > ArgumentError: syntax error on line 2, col -1: `: test

’  
from /usr/lib/ruby/1.8/yaml.rb:133:in `load' from /usr/lib/ruby/1.8/yaml.rb:133:in `load’  
from (irb):7

> >

YAML can’t convert the string it just produced to a Hash. I’ve been able  
(with  
blind trials and using the documentation at  
[http://yaml4r.sourceforge.net/cookbook/](http://yaml4r.sourceforge.net/cookbook/), in particular the section on  
ranges)  
to modify the string produced by dump to make it load again. The  
original  
string is:

* * *

!ruby/object:C ? {}  
: test

The modified one is:

* * *

? !ruby/object:C {}  
: test

It seems that the problem arises from the fact that the dump puts the ?  
(which, if I understand correctly, should mark a hash key) after the  
type of  
the object (the !ruby/object:C part), while load (correctly, I think)  
wants  
it before the type.

There is a bug report for this problem:  
[http://rubyforge.org/tracker/?group\_id=426&atid=1698&func=detail&aid=8886](http://rubyforge.org/tracker/?group_id=426&atid=1698&func=detail&aid=8886)

Stefano

---

<div class="post-metadata">

**Author:** ![thebox](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/91b2a8/32.png) [@thebox](https://www.ruby-forum.com/u/thebox)\
**Post date:** [March 3, 2007, 11:50pm UTC](https://www.ruby-forum.com/t/yaml-issue-with-set/87509/3 "2007-03-03T23:50:58Z")

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On Mar 3, 11:07 am, Stefano C. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> As far as I can tell (I’m not a YAML expert), no. I’ve made a few trials, and  
> it seems that class Hash (which is used internally by Set), has problems with  
> loading / dumping when keys are custom classes. For instance, using irb  
> (ruby -v gives ruby 1.8.5 (2006-12-25 patchlevel 12) [i686-linux], on gentoo)  
> :

[…]

> There is a bug report for this problem:[http://rubyforge.org/tracker/?group\_id=426&atid=1698&func=detail&aid=](http://rubyforge.org/tracker/?group_id=426&atid=1698&func=detail&aid=)…

Thanks, this makes a lot of sense. I’ll stay away from Hash-based  
collection with custom classes and YAML for now.

Giuliano