Re: Closures versus objects

On 16 Feb 2007, at 04:35 pm, [email protected] wrote:
>> non-pure dynamic object code has type
>> dependencies, which are at odds with code reuse and flexibility.

> Regardless I am puzzled by your last sentence.  What dependencies are
> you talking about?

Consider the function:

	list_move_first_to_last = function(list) { list_at_insert(list, 0,  
list_pop_last(list)) }

Notice how each of those functions is dependent on the list type.

Now consider a collection method like:

	Sequence moveLastToFirst := method(atInsert(0, popLast))

in a dynamic OO language, where the method calls are dynamically  
bound, that method could work on *any* object that implements  
atInsert and popLast - be it a Vector, a String, a SortedMap, a List,  
etc. This reusability is the result of dynamic binding.

Now we can do dynamic binding with functions:

	Object_add_method(Collection, Collection_move_first_to_last, function 
(collection)
	{ Object_send(collection, Collection_at_insert, 0, Object_send 
(collection, Collection_pop_last)) }

Now we get the benefits of dynamic binding, but at the cost of (at  
least) mixed semantics.

- Steve