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/*
* Helper function for memoization
*
* The passed labeller function must generate unique and exact names for entries that are naturally equal.
* IDs are persistent.
*
* names, idByName, and entries are accessible fields from the memoizer.
* Behaviour on external modification of these fields is undefined.
*
* An entry object passed to the memoizer has its field "id" set to the memoized id by default.
* The name of the ID field can be modified by calling the getter/setter idField() from the memoizer.
* Behaviour on changing the ID field used while the memoizer has already performed memoization is undefined.
*/
function memoize(labeller) {
var idField = "id";
var names = [];
var idByName = {};
var entries = [];
var _memoizer = function(entry) {
var name = labeller(entry);
if (name in idByName) {
/* We already have a suitable entry. */
var id = idByName[name];
return entries[id];
}
/* New entry. */
/* Set the entry's ID. */
entry[idField] = entries.length;
/* Index the new entry. */
idByName[name] = entry[idField];
names[entry[idField]] = name;
entries.push(entry);
return entry;
}
_memoizer.names = function() { return names; };
_memoizer.idByName = function() { return idByName; };
_memoizer.entries = function() { return entries; };
_memoizer.idField = function(x) {
if (!arguments.length) return idField;
idField = x;
return _memoizer;
};
return _memoizer;
}
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