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Predicate dispatch
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<p>In <a href="/facts/Computer_programming/QmSsFnu0">computer programming</a>, predicate dispatch is a generalisation of <a href="/facts/Multiple_dispatch/eCYSSjGE">multiple dispatch</a> ("multimethods") that allows the <a href="/facts/Method_(computer_programming)/8kAXxVYs">method</a> to call to be selected at runtime based on arbitrary decidable <a href="/facts/Logical_predicate/5WazAvKF">logical predicates</a> and/or <a href="/facts/Pattern_matching/CEwptMs9">pattern matching</a> attached to a method declaration. </p><p><a href="/facts/Raku_(programming_language)/9eYW7vRJ">Raku</a> supports predicate dispatch using "where" clauses that can execute arbitrary code against any function or method parameter. </p><p><a href="/facts/Julia_(programming_language)/AoB0PJ9C">Julia</a> has a package for it with <i><a href="https://github.com/toivoh/PatternDispatch.jl">PatternDispatch.jl</a></i> but otherwise natively supports multiple dispatch. </p><p>Experimental implementations have been created for <a href="/facts/Common_LISP/mq1pRbSF">Common LISP</a>, and for <a href="/facts/Java_(programming_language)/9ScgFyAL">Java</a> (JPred). </p><p>It allows open extension of previously declared methods at a fine-grained level, but multiple extensions with identical or overlapping predicates created by different developers may interfere with each other in unanticipated ways. In this respect it is similar to <a href="/facts/Aspect-oriented_programming/HK7CFwan">aspect-oriented programming</a>. </p>