You could use Clojure protocols.
(defprotocol Rect
(upper-left [this])
(lower-right [this])
(area [this]))
(defn rect1 [x y width height]
(reify Rect
(upper-left [_] [x y])
(lower-right [_] [ (+ width x) (+ width y)])
(area [_] (* width height))))
(defn rect2 [x y width height]
(let [lr [(+ width x) (+ width y)]]
(reify Rect
(upper-left [_] [x y])
(lower-right [_] lr)
(area [_] (* width height)))))
On Thursday, March 5, 2015 at 4:48:11 PM UTC+1, Felix E. Klee wrote:
>
> Disclaimer: I’ve never done *any* Clojure programming, but I’m curious.
>
> Here’s how I may model an on-screen rectangle in JavaScript, a classless
> object oriented language:
>
> let createRectangle = function (x, y, width, height) {
> return {
> get upperLeft() {
> return [x, y];
> },
> get lowerRight() {
> return [x + width, y + height];
> },
> get area() {
> return width * height;
> }
> };
> };
>
> let r = createRectangle(0, 0, 50, 20);
> let s = createRectangle(10, 20, 40, 5);
> console.log(r.upperLeft, r.lowerRight, r.area);
> console.log(s.upperLeft, s.lowerRight, s.area);
>
> Now I run the profiler. I discover that in the inner loop of my program
> there are lots of calls needing the upper left and the lower right
> coordinates. So I change the inner workings of the object to store these
> instead:
>
> let createRectangle = function (x, y, width, height) {
> let upperLeft = [x, y], lowerRight = [x + width, y + height];
>
> return {
> get upperLeft() {
> return upperLeft;
> },
> get lowerRight() {
> return lowerRight;
> },
> get area() {
> return (lowerRight[0] - upperLeft[0]) *
> (lowerRight[1] - upperLeft[1]);
> }
> };
> };
>
> Boom: Now the program is twice as fast, and - what gives me great
> comfort - I know that this change breaks nothing. I only had to edit the
> code in *one* module. I didn’t need to think too much about efficiency
> of data structures in the beginning. I could just start going, then
> optimize in the end.
>
> *Can I program in a similar way using Clojure?*
>
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