Predicate dispatch

In computer programming, predicate dispatch is a generalisation of multiple dispatch ("multimethods") that allows the method to call to be selected at runtime based on arbitrary decidable logical predicates and/or pattern matching attached to a method declaration.^[1][2]

Raku supports predicate dispatch using "where" clauses that can execute arbitrary code against any function or method parameter.^[3]

Julia has a package for it with PatternDispatch.jl but otherwise natively supports multiple dispatch.

Experimental implementations have been created for Common LISP,^[4][5] and for Java (JPred^[2]).

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 aspect-oriented programming.