Another use case that I believe will be common is the following one:
```js
// current state of the art
const result = dbQuery(data)?.rows ?? 'did it just failed or what?';
// VS the "mice operator"
const result = dbQuery(data)<?.rows;
// if it was rows
if (Array.isArray(result))
console.log(result);
else if (result instanceof Error)
console.error(result.message);
else
console.warn(`unexpected result: ${result}`);
```
Ideally, the "mice" should grant chaining up to its latest presence, but I
wouldn't know right now how to reference to it ...
```js
// if no ?? is needed, this might work
const result = dbQuery(data)<?.rows?.data?.entry;
// if ?? is needed, no idea how to back-reference the latest successfull
"mice" result
```
On Thu, Sep 5, 2019 at 11:44 PM Tab Atkins Jr. <[email protected]> wrote:
> On Thu, Sep 5, 2019 at 2:39 PM Andrea Giammarchi
> <[email protected]> wrote:
> >
> > This is basically a solution to a common problem we have these days,
> where modules published in the wild might have a `default` property, to
> support ESM logic, or not.
> >
> > ```js
> > // current optional chaining logic
> > const imported = exported?.default ?? exported;
> >
> > // my "mice operator" proposal
> > const imported = exported<?.default;
> > ```
> >
> > Semantically speaking, not only `<?` actually looks like a mice, it also
> points at its previous value in case the chaining didn't work.
> >
> > Beside the basic example, the "mice operator" might save CPU cycles when
> it comes to involving more complex expressions, i.e.
> >
> > ```js
> > // current "solution"
> > const thing = require('thing')?.default ?? require('thing');
> >
> > // mice operator
> > const thing = require('thing')<?.default;
> > ```
> >
> > This is also easily tranpilable, so kinda a no-brainer for modern dev
> tools to bring in.
> >
> > TL;DR specially for cases where an accessed property should fallback to
> its source, this operator might save both typing and CPU time whenever it's
> needed.
>
> I find it a rather curious pattern, that I'd never seen before! Is it
> used in anything besides this ESM-compat thing you're talking about?
>
> (Saving CPU cycles is not a convincing argument; it's trivial to write
> such a line over two declarations and avoid any expensive
> recomputations.)
>
> ~TJ
>
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