A tiny Clojure library consisting of a single macro
with-redef-methods that allows you to stub defmethod multi-method
bodies. Like Clojure's with-redefs but for defmethods, not vars.
The main use case is for tests, where you want to stub out a specific defmethod for a particular dispatch value.
In particular it was written to aid testing integrant allowing you to selectively stub out small parts of a larger integrant system.
The macro though is fully generic and can be used in any clojure (1.9.0+) code base.
You could for example also use it to introduce new thread local method dispatches. Not that I would recomend such a thing!
WARNING: You may run into some problems using this with ig/load-namespaces
and tools.namespace.
There exists a multi-method with one or more method bodies:
(defmulti wibble (fn [key arg] key)) ;; dispatch on first argument
(defmethod wibble :foo [_ arg]
:foo-body)
(defmethod wibble :bar [_ arg]
:bar-body)
(wibble :foo 1) ;; => :foo-body
(wibble :bar 1) ;; => :bar-body... and you want to stub them thread locally:
(require '[tube-alloys.redef-methods :refer [with-redef-methods]])
(with-redef-methods [wibble {:foo (fn [key arg]
:foo-override)}]
;; Within this thread local dynamic scope (wibble :foo xxx) will trigger our
;; override function and return `:foo-override` instead of the original `defmethod`
;; body.
(wibble :foo 1) ;; => :foo-override
)
;; Outside of the binding scope we get our original implementation:
(wibble :foo 1) ;; => :foo-bodyWeavejester for coming up with the idea whilst discussing approaches to testing integrant systems.
Copyright © 2019 Rick Moynihan
This program and the accompanying materials are made available under the terms of the Eclipse Public License 2.0 which is available at http://www.eclipse.org/legal/epl-2.0.