what is "expr" in serialization methods of collections?

[Paul Johnson]

Jordan Erenreich sent me some new material that we can use in Swarm to 
allow serialization of Arrays.  I'm trying to see how this can be 
finalized and I'm looking at List.m and Map.m and trying to understand 
the way the serialization methods are used. I suppose if I was in a 
research team we would talk this over at lunch, but I'm not, so I ask 
here for open opinions.

In many methods of swarm's collections library, such as lispIn: or 
lispInCreate:, the input is "expr".  Is expr always a Swarm List? I 
trace the calls on this back to defobj.m, but I don't understand how to 
predict what exactly expr is.

Why is it worth knowing?

To do Lisp input in Array.m, suppose I want to adapt the lispIn: method 
from List.m.  We want to iterate over the elements of expr, and ignore 
the ones that are keyword flags, and put the other objects into our 
Array. I have to expand the Array for each item to be added, but I keep 
thinking there's got to be a way to get the "expr" to tell me how many 
objects it has. If I could be sure there was exactly one keyword, for 
example, I could resize the Array in a single shot:

- lispIn: expr
{
  id index, member;
  int c_count = count; //n of objects currently in Array
  int expr_count = [expr getCount]; //n in expr 

  index = [(id) expr begin: scratchZone];
        
        //expand array (self) for new members
        //minus one is for the keyword, if there were only one
  [self setCount: ([self getCount] + expr_count -1 )];

  for (member = [index next]; [index getLoc] == Member; member = [index 
next])
    if (keywordp (member))
      [index next];
    else {
        block[c_count] =  lispIn ([self getZone], member)];
        c_count++;
    }
  [index drop];
  return self;
}

I suppose the worst case scenario is that I resize the Array once to 
have count+expr_count elements, and then after I go over the set of 
inputs, I can shorten the Array back down to count+c_count.

Totally off base?


--
Paul E. Johnson                       email: address@hidden
Dept. of Political Science            http://lark.cc.ku.edu/~pauljohn
University of Kansas                  Office: (785) 864-9086
Lawrence, Kansas 66045                FAX: (785) 864-5700


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