It will work for 0 if you use `number` instead of `js/Number`. Generally
you shouldn't extend any js/* type
On Friday, June 6, 2014 9:57:38 AM UTC-7, Karsten Schmidt wrote:
>
> I'm trying to extend-protocol for numbers and various other types (incl.
> collections & nil) in CLJS, so have been doing something like this (reduced
> email version):
>
> (defprotocol PDeltaEq (delta= [a b]))
>
> (extend-protocol PDeltaEq
> js/Number
> (delta= [a b] :yay)
>
> nil
> (delta= [_ b] (nil? b)))
>
> (delta= 1 1)
> ;; :yay
>
> (delta= 0 0)
> Error: No protocol method Foo.foo defined for type number: 0
>
> Now I guessed, this might have something to do with JS' considering 0 as
> `false` somewhere in the internal protocol machinery... and I was right!
> Here's a relevant excerpt from the compiled protocol dispatch fn:
>
> var delta_EQ___2 = function(a, b) {
> if (function() {
> var and__3466__auto__ = a;
> if (and__3466__auto__) {
> return a.thi$ng$common$math$core$PDeltaEq$delta_EQ_$arity$2;
> } else {
> return and__3466__auto__;
> }
> }()) {
> return a.thi$ng$common$math$core$PDeltaEq$delta_EQ_$arity$2(a, b);
> } else {
> ....
> }
> };
>
> Obviously, with the `a` arg being 0, that `if (and__3466__auto__)` check
> is always failing, so shouldn't this check be rewritten as:
>
> if (goog.isDefAndNotNull(and__3466__auto__) &&
> a.thi$ng$common$math$core$PDeltaEquals$delta_EQ_$arity$2) {
> return a.thi$ng$common$math$core$PDeltaEquals$delta_EQ_$arity$2;
> }
> ...
>
> This change seems to fix this kind of error and AFAIK doesn't impact any
> of my other (30+) test cases for this protocol...
>
> Thoughts? :)
>
> Thanks, K.
>
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