feat(defmulti): allow .add() to overwrite existing impl, add logger

- update .add() to log warning msg when overwriting existing impl
- add LOGGER, setLogger()
- update tests / readme

packages/defmulti/README.md

@@ -46,7 +46,8 @@ varargs solution.
 The function returned by `defmulti` can be called like any other
 function, but also exposes the following operations:
 
-- `.add(id, fn)` - adds new implementation for given dispatch value
+- `.add(id, fn)` - adds/overrides implementation for given dispatch
+  value
 - `.remove(id)` - removes implementation for dispatch value
 - `.callable(...args)` - takes same args as if calling the
   multi-function, but only checks if an implementation exists for the

packages/defmulti/src/api.ts

@@ -8,7 +8,9 @@ import {
     Fn7,
     Fn8,
     FnAny,
-    IObjectOf
+    ILogger,
+    IObjectOf,
+    NULL_LOGGER
 } from "@thi.ng/api";
 
 export const DEFAULT: unique symbol = Symbol();
@@ -303,3 +305,7 @@ export interface MultiFn8O<A, B, C, D, E, F, G, H, I, T>
         MultiFnBase<Implementation8O<A, B, C, D, E, F, G, H, I, T>> {}
 
 export type AncestorDefs = IObjectOf<Iterable<PropertyKey>>;
+
+export let LOGGER: ILogger = NULL_LOGGER;
+
+export const setLogger = (logger: ILogger) => (LOGGER = logger);

packages/defmulti/src/defmulti.ts

@@ -21,6 +21,7 @@ import {
     DispatchFn8,
     DispatchFn8O,
     Implementation,
+    LOGGER,
     MultiFn,
     MultiFn1,
     MultiFn1O,
@@ -105,7 +106,9 @@ export function defmulti<T>(f: any, ancestors?: AncestorDefs) {
             : unsupported(`missing implementation for: "${id.toString()}"`);
     };
     fn.add = (id: PropertyKey, g: Implementation<T>) => {
-        if (impls[<any>id]) return false;
+        if (impls[<any>id]) {
+            LOGGER.warn(`overwriting '${id.toString()}' impl`);
+        }
         impls[<any>id] = g;
         return true;
     };

packages/defmulti/test/index.ts

@@ -1,9 +1,11 @@
+import { ConsoleLogger } from "@thi.ng/api";
 import * as assert from "assert";
 import {
     DEFAULT,
     defmulti,
     defmultiN,
-    implementations
+    implementations,
+    setLogger
 } from "../src/index";
 
 // prettier-ignore
@@ -26,10 +28,14 @@ describe("defmulti", () => {
         assert(exec.add("+", ([_, ...args]) => args.reduce((acc: number, n: any) => acc + exec(n), 0)));
         assert(exec.add("*", ([_, ...args]) => args.reduce((acc: number, n: any) => acc * exec(n), 1)));
         assert(exec.add("number", (x) => x));
-        assert(!exec.add("number", (x) => x));
         assert(exec.add(DEFAULT, (x) => { throw new Error(`invalid expr: ${x}`); }));
 
         assert.equal(exec(["+", ["*", 10, ["+", 1, 2, 3]], 6]), 66);
+
+        setLogger(new ConsoleLogger("defmulti"));
+        assert(exec.add("number", (x) => x * 2));
+        assert.equal(exec(["+", ["*", 10, ["+", 1, 2, 3]], 6]), ((1*2 + 2*2 + 3*2) * 10*2) + 6*2);
+
         assert.throws(() => exec(""));
     });