Le 20 août 2014 à 10:42, Andy Wingo <wi...@igalia.com> a écrit :
> On Tue 19 Aug 2014 08:48, Claude Pache <claude.pa...@gmail.com> writes:
>
>> Le 19 août 2014 à 06:47, Kevin Smith <zenpars...@gmail.com> a écrit :
>>
>> It appears that the current state of affairs is that the argument
>> supplied to the first call of `next` on a newborn generator is
>> "ignored and inaccessibe".
>>
>> Is there any way that the generator function can have access to that
>> lost data?
>>
>> This can be worked around. Basically, ask the generator to advance to
>> the first `yield` at instantiation, and retrieve the value of the
>> "first" `next()` with that `yield`. For example:
>
> This has the disadvantage of starting computation in the generator, of
> course, before it has been asked for.
>
Indeed. Here is a version that don't start computation early.
```js
const ignoreFirst = genFn => class extends genFn {
next(x) {
delete this.next // next calls to `next` will use directly the super
method
super()
return super(x)
}
}
var echo = ignoreFirst(function* echo() {
var x
while (true) {
x = yield x
}
})
var iter = new echo // note: `new` is needed for correct subclassing!
iter.next(4) // {value: 4, done: false}
iter.next(1) // {value: 1, done: false}
iter.next(6) // {value: 6, done: false}
```
—Claude
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