Operator overloading for non-value objects

Brendan Eich brendan at mozilla.com
Tue Jan 14 12:49:44 PST 2014


Kevin Smith wrote:
>
>     `0m` is literal syntax, for `decimal(0)`. Where `decimal` is a
>     value type factory.
>
>
> Right - I meant what are the semantics of "===" applied to dissimilar, 
> perhaps "numeric", value types.

We worked through this in 2008 when IBM was pushing decimal at ES3.1 
(now ES5). We do not want 0m === 0 for many reasons, including the relation

   typeof x == typeof y && x == y <=>  x === y

We also didn't want problems of cohorts differing by significance (1.0m 
vs. 1m, if you can believe it) being equated to 1 (the number).

This is one of the reasons I've designed value objects (so far) to allow 
typeof customization. (The other is because typeof is *useful* in 
numeric contexts, and making all non-number numerics have typeof-type 
"object" is useless, a disservice to users.)

There is nothing wrong in my view with well-written == usage. I'm not 
Crock. I don't say always use ===. While opinions vary, the fact remains 
that == and <= are in the language, are loose, and need to be 
overloadable for useful value objects, specifically more numeric types. 
Suggest you pull == out of your mental penalty box and look at it again. 
It's not a recidivist.

/be


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