[Siop-development] Passing by value and by reference

[Rapheal K. <ra...@ma...>]

  I've added a "ref" and "val"... err... modifier?  Not sure what to call 
them.  They are intended to be simple markers that a host language can use as 
a hint to the bridge so that the bridge knows to over-ride the default 
parameter behavior for an object being passed to a peer either via parameters 
or return value.

  Remember, scalar values are passed by value by default while collections are 
passed by reference by default.  These little keyword thingies can over-ride 
this default behavior.  So, let's say you were calling a method that uses a 
list.  It might be the case that the programmer can figure out that it would 
be an optimization to send the list to the other side, especially if the code 
over there does a lot of random access:

  remote_object.helpful_method( val( [ "a", "b", "c", "d" ] ) )

  The example above would send a reference to the list if it were not for the 
modifier wrapper object.

  This is very useful in the example wxWidgets code where we needed to 
construct native Python tuples and dictionaries in order to be able to create 
new classes:

    # Helper method to define Python types
    # Class creation requires actual Python tuples, not pretenders
    # TODO: This can be disposed of when it is possible to pass
    # tuples by-value
    def tuple( *stuff  )
        list = $types.ListType.call
        for thing in stuff
            list.append( thing )
        end
        $types.TupleType( list )
    end

    # Helper method to define Python class
    # In the future, may provide helper library to do this
    def pyclass( name, *parents, &definition )
        klass = $types.ClassType(   name.to_s,
                                tuple( *parents ),
                                $types.DictType.call
                                )
        klass.instance_eval &definition unless definition.nil?
        klass
    end


  Now it's a little easier:


    # Helper method to define Python class
    # In the future, may provide helper library to do this
    def pyclass( name, *parents, &definition )
        klass = $types.ClassType(   name.to_s,
                                Siop::val( Siop::Tuple( *parents ) ),
                                Siop::val( {} )
                                )
        klass.instance_eval &definition unless definition.nil?
        klass
    end

  Anyone who thinks they follow this and cares to voice their opinion as to 
wether this seems ok or is cumbersome, or thinks there might be a more 
preferable way, please tell me.

  - Rafe