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copied!<p>Here is a generic <a href="http://en.wikipedia.org/wiki/Memoization" rel="noreferrer">memoization</a> solution that is compatible with PHP 5.2.x.</p> <p>The call_memoized function:</p> <ol> <li>Generates a unique cache key based on the function name and arguments.</li> <li>If the cache is empty, invokes the function and updates the cache with the result.</li> <li>Returns the cached value.</li> </ol> <p>Instead of using call_memoized directly, use the provided memoize function, which returns a new version of the given function that will automatically cache results from the same combination of parameters.</p> <p>See example below.</p> <p>Enjoy!</p> <pre class="lang-php prettyprint-override"><code>global $MEMO_CACHE; $MEMO_CACHE = array(); /** Returns the result of the function with the given arguments. * Invokes the function only once, thereafter returns the result * cached by a key based on the function name and arguments. */ function call_memoized($fun, $args=array()) { global $MEMO_CACHE; // generate a cache key based on the function name and arguments $uid = md5( implode("|", array_merge((array)$fun, array_map( "serialize", $args) )) ); // if there result hasn't been cached, call the function // and update the cache with the result. if(!array_key_exists($uid, $MEMO_CACHE)) { $MEMO_CACHE[$uid] = call_user_func_array($fun, $args); } return $MEMO_CACHE[$uid]; } /** Returns a memoized version of the given function that will cache * its results for each unique set of inputs. */ function memoize($fun) { return create_function( '', "\$args = func_get_args(); return call_memoized('$fun', \$args);" ); } </code></pre> <p><strong>Example:</strong></p> <pre class="lang-php prettyprint-override"><code>/** Returns a random number with the given greeting. */ function random($greeting) { return "$greeting! " . rand(); }; print("Five random numbers:</br />"); for($i=0; $i<5; $i++) { print(random("Spin the wheel") . "<br />"); } print "<br />"; print("After memoizing the random function, it's not so random:<br />"); $not_so_random = memoize("random"); for($i=0; $i<5; $i++) { print($not_so_random("Spin the wheel") . "<br />"); } print "<br />"; print("The same memoized function is invoked with a different argument, and thus creates a different cache key:<br />"); for($i=0; $i<5; $i++) { print($not_so_random("Twirl the tire") . "<br />"); } /* OUTPUT Five random numbers: Spin the wheel! 26488 Spin the wheel! 20049 Spin the wheel! 14006 Spin the wheel! 28599 Spin the wheel! 804 After memoizing the random function, it's not so random: Spin the wheel! 32397 Spin the wheel! 32397 Spin the wheel! 32397 Spin the wheel! 32397 Spin the wheel! 32397 The same memoized function is invoked with a different argument, and thus creates a different cache key: Twirl the tire! 2114 Twirl the tire! 2114 Twirl the tire! 2114 Twirl the tire! 2114 Twirl the tire! 2114 */ </code></pre>

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