Asp Forum - Marshal.dump fails on extended OpenStruct

synergism

2/17/2009 6:31:00 PM

If I subclass OpenStruct and extend the subclass, I cannot
Marshal.dump it. This is apparently because ostruct.rb has its own
custom marshal_dump / marshal_load that only cares about what's in
@table:

def marshal_dump
@table
end
def marshal_load(x)
@table = x
@table.each_key{|key| new_ostruct_member(key)}
end

Is there no way to fix this in ostruct.rb to allow my 'bad' example
below to work?

require 'pp'
require 'ostruct'

case ARGV.first
when /bad/i,nil
class C < OpenStruct
def initialize
super()
@var=123
end
end
when /good/i
class C
def initialize
@struct=OpenStruct.new
@var=123
end

def method_missing method,*args,&block
@struct.send method,*args,&block
end
end
end

c=C.new
c.a=:a
pp c
puts 'c.a=%s ' % c.a
puts 'c var=%s' % c.instance_variable_get('@var')
x=Marshal.load(Marshal.dump(c))

pp x
puts 'x.a=%s ' % x.a
puts 'x var=%s' % x.instance_variable_get('@var')

4 Answers

Justin Collins

2/17/2009 8:33:00 PM

synergism wrote:
> If I subclass OpenStruct and extend the subclass, I cannot
> Marshal.dump it. This is apparently because ostruct.rb has its own
> custom marshal_dump / marshal_load that only cares about what's in
> @table:
>
> def marshal_dump
> @table
> end
> def marshal_load(x)
> @table = x
> @table.each_key{|key| new_ostruct_member(key)}
> end
>
> Is there no way to fix this in ostruct.rb to allow my 'bad' example
> below to work?
>
> require 'pp'
> require 'ostruct'
>
> case ARGV.first
> when /bad/i,nil
> class C < OpenStruct
> def initialize
> super()
> @var=123
> end
> end
> when /good/i
> class C
> def initialize
> @struct=OpenStruct.new
> @var=123
> end
>
> def method_missing method,*args,&block
> @struct.send method,*args,&block
> end
> end
> end
>
> c=C.new
> c.a=:a
> pp c
> puts 'c.a=%s ' % c.a
> puts 'c var=%s' % c.instance_variable_get('@var')
> x=Marshal.load(Marshal.dump(c))
>
> pp x
> puts 'x.a=%s ' % x.a
> puts 'x var=%s' % x.instance_variable_get('@var')
>
>

You could just write new marshal_dump and marshal_load methods:

require 'ostruct'
require 'pp'
class C < OpenStruct

def initialize *args
super
@var = 123
end

def marshal_dump
[@table, Hash[self.instance_variables.map { |v| [v, self.instance_variable_get("#{v}")] }]]
end

def marshal_load x
@table = x[0]
@table.each_key{|key| new_ostruct_member(key)}
x[1].each do |k,v|
self.instance_variable_set("#{k}", v) unless k.to_sym == :table
end
end
end

c=C.new
c.a=:a
pp c
puts 'c.a=%s ' % c.a
puts 'c var=%s' % c.instance_variable_get('@var')
x=Marshal.load(Marshal.dump(c))

pp x
puts 'x.a=%s ' % x.a
puts 'x var=%s' % x.instance_variable_get('@var')

-Justin

Justin Collins

2/17/2009 8:52:00 PM

Justin Collins wrote:
> synergism wrote:
>> If I subclass OpenStruct and extend the subclass, I cannot
>> Marshal.dump it. This is apparently because ostruct.rb has its own
>> custom marshal_dump / marshal_load that only cares about what's in
>> @table:
>>
>> def marshal_dump
>> @table
>> end
>> def marshal_load(x)
>> @table = x
>> @table.each_key{|key| new_ostruct_member(key)}
>> end
>>
>> Is there no way to fix this in ostruct.rb to allow my 'bad' example
>> below to work?
>>
>> require 'pp'
>> require 'ostruct'
>>
>> case ARGV.first
>> when /bad/i,nil
>> class C < OpenStruct
>> def initialize
>> super()
>> @var=123
>> end
>> end
>> when /good/i
>> class C
>> def initialize
>> @struct=OpenStruct.new
>> @var=123
>> end
>>
>> def method_missing method,*args,&block
>> @struct.send method,*args,&block
>> end
>> end
>> end
>>
>> c=C.new
>> c.a=:a
>> pp c
>> puts 'c.a=%s ' % c.a
>> puts 'c var=%s' % c.instance_variable_get('@var')
>> x=Marshal.load(Marshal.dump(c))
>>
>> pp x
>> puts 'x.a=%s ' % x.a
>> puts 'x var=%s' % x.instance_variable_get('@var')
>>
>>
>
>
Let me try that again:

require 'ostruct'
require 'pp'

class C < OpenStruct

def initialize *args
super
@var = 123
end
def marshal_dump
[@table, Hash[self.instance_variables.map { |v| [v,
self.instance_variable_get("#{v}")] }]]
end
def marshal_load x
@table = x[0]
@table.each_key{|key| new_ostruct_member(key)}
x[1].each do |k,v|
self.instance_variable_set("#{k}", v) unless k.to_sym == :table
end
end
end

c=C.new
c.a=:a
pp c
puts 'c.a=%s ' % c.a
puts 'c var=%s' % c.instance_variable_get('@var')
x=Marshal.load(Marshal.dump(c))

pp x
puts 'x.a=%s ' % x.a
puts 'x var=%s' % x.instance_variable_get('@var')

Justin Collins

2/17/2009 8:57:00 PM

Justin Collins wrote:
> Justin Collins wrote:
>> synergism wrote:
>>> If I subclass OpenStruct and extend the subclass, I cannot
>>> Marshal.dump it. This is apparently because ostruct.rb has its own
>>> custom marshal_dump / marshal_load that only cares about what's in
>>> @table:
>>>
>>> def marshal_dump
>>> @table
>>> end
>>> def marshal_load(x)
>>> @table = x
>>> @table.each_key{|key| new_ostruct_member(key)}
>>> end
>>>
>>> Is there no way to fix this in ostruct.rb to allow my 'bad' example
>>> below to work?
>>>
>>> require 'pp'
>>> require 'ostruct'
>>>
>>> case ARGV.first
>>> when /bad/i,nil
>>> class C < OpenStruct
>>> def initialize
>>> super()
>>> @var=123
>>> end
>>> end
>>> when /good/i
>>> class C
>>> def initialize
>>> @struct=OpenStruct.new
>>> @var=123
>>> end
>>>
>>> def method_missing method,*args,&block
>>> @struct.send method,*args,&block
>>> end
>>> end
>>> end
>>>
>>> c=C.new
>>> c.a=:a
>>> pp c
>>> puts 'c.a=%s ' % c.a
>>> puts 'c var=%s' % c.instance_variable_get('@var')
>>> x=Marshal.load(Marshal.dump(c))
>>>
>>> pp x
>>> puts 'x.a=%s ' % x.a
>>> puts 'x var=%s' % x.instance_variable_get('@var')
>>>
>>>
>>
>>
> Let me try that again:
>
> require 'ostruct'
> require 'pp'
>
> class C < OpenStruct
>
> def initialize *args
> super
> @var = 123
> end def marshal_dump
> [@table, Hash[self.instance_variables.map { |v| [v,
> self.instance_variable_get("#{v}")] }]]
> end def marshal_load x
> @table = x[0]
> @table.each_key{|key| new_ostruct_member(key)}
> x[1].each do |k,v|
> self.instance_variable_set("#{k}", v) unless k.to_sym == :table
> end
> end
> end
>
> c=C.new
> c.a=:a
> pp c
> puts 'c.a=%s ' % c.a
> puts 'c var=%s' % c.instance_variable_get('@var')
> x=Marshal.load(Marshal.dump(c))
>
> pp x
> puts 'x.a=%s ' % x.a
> puts 'x var=%s' % x.instance_variable_get('@var')
>

I give up. I don't know why the formatting is all weird.

-Justin

synergism

2/19/2009 11:21:00 AM

On Feb 17, 4:32 pm, Justin Collins <justincoll...@ucla.edu> wrote:
> You could just write new marshal_dump and marshal_load methods:

Thanks. I considered that, but the bigger issue is that this makes
using DRb in any application of non-trivial complexity quite painful,
as we now need to mess with the implementation details of every
serialized object. I was just hoping something more transparent could
be done with ostruct to make things better.

Incidentally, I continued with the delegation model I used in my
example and found that this wasn't where the trouble ended. I had to
also eliminate an un-dumpable proc I had used to auto-initialize a
Hash of Hashes (to make an empty hash be the default value so that []
[] references would not raise an exception on uninitialized keys) i.e.

class AutoHash < Hash
def [] key
_=fetch(key) rescue _=store(key,{})
_
end
end

class C
def initialize
# ...
@attributes=AutoHash.new
end
end

instead of:

# ...
@attributes=Hash.new{|hash,key| hash[key]={}}

It seems programming with DRb is fraught with difficulties like
these. I wish we had something easier to use, as otherwise DRb is
exactly what we need for this application.

Ben

comp.lang.ruby

Marshal.dump fails on extended OpenStruct

synergism

Justin Collins

Justin Collins

Justin Collins

synergism

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