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The Ashes
Technology, Science and other news
May 10, 2009
A Better Javascript Memoizer
Filed under : General
We have covered memoizers in the past, but John Hann has posted on a nice implementation that takes advantage of closures, arity, and recursion — 3 concepts/features that Javascript was meant to use.
It leads to this generic version:
JAVASCRIPT:
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// memoize: a general-purpose function to enable a function to use memoization
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// func: the function to be memoized
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// context: the context for the memoized function to execute within
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// Note: the function must use explicit, string-serializable parameters
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function memoize (func, context) {
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function memoizeArg (argPos) {
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var cache = {};
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return function () {
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if (argPos == 0) {
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if (!(arguments[argPos] in cache)) {
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cache[arguments[argPos]] = func.apply(context, arguments);
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}
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return cache[arguments[argPos]];
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}
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else {
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if (!(arguments[argPos] in cache)) {
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cache[arguments[argPos]] = memoizeArg(argPos – 1);
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}
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return cache[arguments[argPos]].apply(this, arguments);
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}
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}
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}
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// JScript doesn’t grok the arity property, but uses length instead
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var arity = func.arity || func.length;
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return memoizeArg(arity – 1);
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}
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and this conclusion:
Yes, memoization is a neat concept. But why use it rather than just hand-coded caching mechanisms? It’s easy enough to write a caching routine, right? Here are a few good reasons:
- hand-coded caching mechanisms obfuscate your code
- multi-variate caching routines are bulky in Javascript
- fewer lines of code means fewer bugs
- Java programmers will think more highly of you
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