Subject: [xsl] ($possibly-empty, $default)[1] idiom optimisation From: Andrew Welch <andrew.j.welch@xxxxxxxxx> Date: Wed, 24 Mar 2010 10:21:22 +0000 |
Hi, This is often used as a nice way to avoid an if-then-else check to display $default if $possibly-empty is empty: ($possibly-empty, $default)[1] Out of interest, is it likely to be optimised to avoid evaluating $default if the first item is not empty, because if $default takes a reasonable amount of work to evaluate it's effectively wasted most of the time (if $default is rare). If it takes more work to evaluate $default than to test whether $possibly-empty is empty each time, then this is just a short cut rather than good practice. It reminds me of advice I heard (for Java) to wrap all log statements in an if test to check the log level first to avoid the unnecessary creation of the log message. For example, constructing a large message for a debug log by combining several different things, only for the constructed string to be discarded because the log level is info. (testing the log level a 1000 times is far better than creating and discarding 1000 strings) -- Andrew Welch http://andrewjwelch.com Kernow: http://kernowforsaxon.sf.net/
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