-- Copyright 1993-1998, by the Cecil Project
-- Department of Computer Science and Engineering, University of Washington
-- See the LICENSE file for license information.


-- a simple identity table that tracks which collections are currently being
-- iterated through using *_allowing_updates.

concrete object allowing_updates isa identity_assoc_table[any, int];
  method begin_allowing_updates(t@:allowing_updates, table:any):void {
      t!table := t.fetch(table, { 0 }).succ;
  }
  method done_allowing_updates(t@:allowing_updates, table:any):void {
      let count:int := (t!table).pred;
      if(count = 0, {
	  t.remove_key(table);
      }, {
	  t!table := count;
      });
  }
  method updates_allowed(t@:allowing_updates, table:any):bool {
      t.includes_key(table) }