On Oct 28, 12:46 pm, Howard Lewis Ship <hls...@gmail.com> wrote: > (extend-type Asset > ToAttributeValueString > (to-attribute-value-string [asset] (:client-url asset)))
As Alex mentioned we have an "adapt-protocol" macro [1] [2] that I think will do what you want. It would be invoked as: (adapt-protocol Asset ToAttributeValueString (to-attribute-value-string [asset] (client-url asset))) >From your original code, I changed "extend-type" to "adapt-protocol" and I fixed what I think is a type by changing ":client-url" to "client-url". There are different ways to think of what this does. One way is to think of adapting one protocol to another. The adapt-protocol call defines how to adapt an Asset object to an ToAttributeValueString object. Another way is to think of layering the protocols. The ToAttributeValueString protocol is layered on top of the Asset protocol by defining how to satisfy the ToAttributeValueString protocol in terms of the Asset protocol. At a lower level what this adapt-protocol call means is: for any type that implements Asset but does not already implement ToAttributeValueString, add an implementation of Asset to that type using the provided functions. This implementation will be added the first time that an attempt is made to access the type via the ToAttributeValueString protocol. It is useful to be able to define this in one place rather than tracking down all of the types that implement the Asset protocol and extending them to support the ToAttributeValueString protocol. I don't think it is useful to try and think of this as interface inheritance because it is not the same as interface inheritance in Java. We are using this code in production to do exactly what you described. The only real issue to be aware of is that once an adapter is “installed” for a class subsequent calls to adapt-protocol do not affect the class. This can cause pain at dev time when you are changing the adapter code and want to dynamically redefine an adapter. I talk about this issue and a way to address it at dev time in the blog post [1]. -David [1] http://david-mcneil.com/post/3495351254/clojure-protocol-adapters [2] https://github.com/david-mcneil/clojure-adapt -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
