On Mon, Apr 20, 2009 at 1:27 PM, Bradbev <brad.beveri...@gmail.com> wrote: > If you promise that > functions will accept and return maps with certain keys, then you must > keep that promise moving forward.
I think you're missing part of the point of the original post. You don't really want to promise that your functions accept and return maps with certain keys; you want to promise that your functions accept and return objects that *act* like maps with certain keys. Promising a map is too specific. You merely want to promise something that behaves like a map. Of course, the simplest thing that acts like a map is a map, so in early stages of development, you're certainly going to use maps. But does such a thing scale when you decide you need something more complex? In the original example, the data has grown from a map that actually contains a :name to something that retrieves a :name indirectly by concatenating :first-name and :last-name. This is a perfectly reasonable example of the way that data representations grow and change over time. Of course, if you had programmed your entire app with getters and setters from the outset, making such a modification is relatively straightforward (see footnote *). But most people aren't going to program that way from the outset. They are going to use maps because that's the easiest thing, and that means they will get and set things using get, assoc, and the syntactic function-like shortcuts for retrieving things from maps. (Footnote * - Well maybe it's not so easy to convert something that uses getters and setters from the outset but still uses a map to hold the data. maps are very "leaky abstractions", and even if you provide getters and setters, it's entirely possible that users might intentionally or unintentionally use something map-specific, rather than adhering to the level of indirection that is needed to make a conversion easy.) But then when you eventually want to alter your data representation, then what do you do? It's certainly possible to make your name objects some sort of proxy for the associative interface, function interface, and anything else relevant to maps, and special case the getting of :name, but that's quite cumbersome. Is there a simple way to do this extension? Not really, and I think this is a legitimate concern. --~--~---------~--~----~------------~-------~--~----~ 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 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 -~----------~----~----~----~------~----~------~--~---
