YAML problem with Method pointers


#1

It looks like YAML can’t restore a Method pointer. True? Or am I doing
something wrong here. Is this a known Ruby bug or a limitation of YAML
or a Larry-is-a-goof problem? The following code frag fails on the last
line when it tries to load the YAML string…

class MyKlass
def initialize
@myMethodPtr = method(:myMethod)
end
def myMethod command
end
end

myObj = MyKlass.new

puts myObj.to_yaml # YAML text generated but it’s missing the Method
Info
$newObj = YAML.load( myObj.to_yaml ) # FAILS HERE

------ OUTPUT ------

— !ruby/object:MyKlass
myMethodPtr: !ruby/object:Method {}

C:/ruby/lib/ruby/1.8/yaml.rb:133:in transfer': allocator undefined for Method (TypeError) from C:/ruby/lib/ruby/1.8/yaml.rb:133:innode_import’
from C:/ruby/lib/ruby/1.8/yaml.rb:133:in load' from C:/ruby/lib/ruby/1.8/yaml.rb:133:inload’
from x_yml_builder.rb:12

Thanks,
Larry F.


#2

Larry F. wrote:

It looks like YAML can’t restore a Method pointer. True? Or am I doing
something wrong here. Is this a known Ruby bug or a limitation of YAML
or a Larry-is-a-goof problem? The following code frag fails on the last
line when it tries to load the YAML string…

Methods can’t be serialized, by Marshal or by YAML. A serialized method
would have to contain the source code of the method (or something
equivalent to the source, such as a parse tree).

Note that Object#method returns a Method object, which will not be
affected if you later redefine #myMethod in MyKlass (see below). So
maybe it is best not to think of it as a pointer or a symbolic
reference, but as a sort of snapshot of the method, including the
definition as well as the “self”.

Is it possible for you to use the method name instead of capturing a
Method object?

class MyKlass
attr_reader :myMethodPtr
def initialize
@myMethodPtr = method(:myMethod)
end
def myMethod
puts “command”
end
end

myObj = MyKlass.new

myObj.myMethodPtr.call

class MyKlass
def myMethod
puts “FOO”
end
end

myObj.myMethodPtr.call

END

Output:

command
command


#3

Thanks Joel,
Since I’m using the method in other classes I switched to sending in the
whole of myObj and then accessing the method. It’s not pretty but it
gets the job done. The snippet below looks OK. I guess my code is only
a mess because the method I want to use is part of a larger class. If I
isolate the method I want the code will probably be cleaner.

Cheers,
Larry

class MethodWrapper
def myMethod
puts “command”
end
end

class OtherKlass
def initialize( methodWrapper )
methodWrapper.myMethod
end
end

myObj = MethodWrapper.new

otherObj = OtherKlass.new(myObj)