Custom marshalling with YAML

[Anders Bengtsson]

Hi,

I've run into a problem when replacing "Marshal.dump" with "YAML.dump".
Some of my classes use custom marshalling, with "_dump" and "_load"
methods. With YAML these methods are not used, which breaks the
application.

YAML uses an object's "to_yaml" method if available. But that method
expects valid YAML code to be returned, unlike "_dump" that can return
just about anything. Also there doesn't seem to be anything
corresponding to "_load".
Any ideas about how I can make things compatible with both Marshal and
YAML at the same time?

/Anders


=====
__________________________________________________
Anders Bengtsson (e-mail address removed)
Stockholm, Sweden

Höstrusk och grå moln - köp en resa till solen på Yahoo! Resor på adressen http://se.docs.yahoo.com/travel/index.html

 

[Michael Neumann]

Hi,

I've run into a problem when replacing "Marshal.dump" with "YAML.dump".
Some of my classes use custom marshalling, with "_dump" and "_load"
methods. With YAML these methods are not used, which breaks the
application.

YAML uses an object's "to_yaml" method if available. But that method
expects valid YAML code to be returned, unlike "_dump" that can return
just about anything. Also there doesn't seem to be anything
corresponding to "_load".
Any ideas about how I can make things compatible with both Marshal and
YAML at the same time?

How about this:

module Kernel
def to_yaml
if respond_to? :_dump
_dump(nil).to_yaml # TODO: _dump takes one paramter
else
raise
end
end
end

_load is a class method!

Regards,

Michael

 

[Anders Bengtsson]

How about this:

module Kernel
def to_yaml
if respond_to? :_dump
_dump(nil).to_yaml # TODO: _dump takes one paramter
else
raise
end
end
end

That would be a nice solution. But the string returned by _dump
probably won't be valid YAML.

If I have the following class

class Foo
def _dump(x)
"foo"
end

def to_yaml
_dump
end
end

then YAML.dump(Foo.new) will return "foo". But that's no good, since
there's nothing to tell it that this "foo" should be de-YAMLed into a
new Foo instance.
Marshal.dump(Foo.new) will return "\004\010u:\010Foo\010foo", with all
the needed meta-data.

_load is a class method!

Yes. But what's the corresponding method for YAML?

/Anders


=====
__________________________________________________
Anders Bengtsson (e-mail address removed)
Stockholm, Sweden

Höstrusk och grå moln - köp en resa till solen på Yahoo! Resor på adressen http://se.docs.yahoo.com/travel/index.html

 

[Michael Neumann]

That would be a nice solution. But the string returned by _dump
probably won't be valid YAML.

If I have the following class

class Foo
def _dump(x)
"foo"
end

def to_yaml
_dump
end
end

Take a look at lib/yaml/rubytypes.rb.

There's a to_yaml_type and a YAML.add_ruby_type method.
Maybe this is a start.

Regards,

Michael

 

[Anders Bengtsson]

Take a look at lib/yaml/rubytypes.rb.

There's a to_yaml_type and a YAML.add_ruby_type method.
Maybe this is a start.

Thanks Michael, the code in rubytypes.rb does indeed look something
like what I'm looking for.

/Anders


=====
__________________________________________________
Anders Bengtsson (e-mail address removed)
Stockholm, Sweden

Höstrusk och grå moln - köp en resa till solen på Yahoo! Resor på adressen http://se.docs.yahoo.com/travel/index.html