It was merely a mention of my work around, and wasn't intended to be perfect (`pipe(f) !== f`). Note the lazy one-liner. I think both Array and Promise both could use this, though. And what do you all think about the name `tap`, for effectively `tap`ping into the pipeline? I would love to see this make it in. It's very easily optimizable.
On Fri, Oct 16, 2015, 15:38 Andrea Giammarchi <[email protected]> wrote: > The "complete" version might look more like the following: > > ```js > function pipe(f) { > return Object.defineProperties( > function (x) { > f.apply(this, arguments); > return x; > }, > { > length: Object.getOwnPropertyDescriptor(f, "length"), > name: Object.getOwnPropertyDescriptor(f, "name") > } > ); > } > ``` > > yet I find this more complicated than just a map and if it is about > immutable then map wins even more. > > I don't see why this is a problem in October 2015, Array#forEach has been > like that since ever. > > Let's move on or maybe discuss a new method? > > Regards > > > > On Fri, Oct 16, 2015 at 7:51 PM, Isiah Meadows <[email protected]> > wrote: > >> What about a `tap` function similar to Bluebird's `tap` function for its >> promises? >> >> I frequently write a `pipe` function that deals with this common case >> (with arrays, but frequently promises and other monadic structures as well). >> >> ```js >> // Complete transparent wrapper >> function pipe(f) { >> function g(x) { >> f.apply(this, arguments) >> return x >> } >> >> return Object.defineProperty(g, "length", >> Object.getOwnPropertyDescriptor(f, "length")) >> } >> >> // My usual lazy version >> function pipe(f) { >> return function (x) { >> f.apply(this, arguments) >> return x >> } >> } >> >> // My super-lazy version >> const pipe = f => x => (f(x), x) >> ``` >> >> On Fri, Oct 16, 2015, 12:52 Kris Kowal <[email protected]> wrote: >> >>> forEach should return undefined. Array-like methods for iterators solve >>> the problem of building unnecessary memory pressure for intermediate maps. >>> >>> The return value of forEach is special. True, for arrays it is always >>> undefined. However, the forEach method on an iterator returned by a >>> generator function should be the return value of the generator. Consider >>> this range generator that returns the number of visited values. >>> >>> ```js >>> function *range(start, stop, step) { >>> for (var index = start; index < stop; stop += step) { >>> yield index; >>> } >>> return (stop - start) / step; >>> } >>> var iterator = range(0, 10, 1); >>> var iterations = iterator.forEach((x) => console.log(x)); >>> console.log(iterations); >>> ``` >>> >>> Kris Kowal >>> >>> On Fri, Oct 16, 2015 at 7:30 AM, Andrea Giammarchi < >>> [email protected]> wrote: >>> >>>> That's usually a made-up issue ... the example code is using two maps >>>> instead of computing the entire thing once in a composed function **and** >>>> it already creates multiple copies of the initial Array. >>>> >>>> Anyway, having `var log = DEBUG ? x => console.log(x) || x : x => x` >>>> in means you could do this: >>>> >>>> ```js >>>> const a = log([1, 2, 3] >>>> .map(square)) >>>> .map(plus1) >>>> .reduce(add); >>>> ``` >>>> >>>> but again, we are using multiple maps and a reduce so if we want to be >>>> realistic, and it's for debugging purpose only, I think using map would be >>>> just fine. >>>> >>>> Regards >>>> >>>> >>>> On Fri, Oct 16, 2015 at 3:17 PM, Eric Devine <[email protected]> >>>> wrote: >>>> >>>>> Array#map does the non-trivial operation of copying the entire array. >>>>> In the example for loging to the console, this behavior is unintended. >>>>> Perhaps an underscore-like tap method should be considered to be added to >>>>> the Array prototype for these cases. >>>>> >>>>> >>>>> On Fri, Oct 16, 2015 at 9:32 AM, Andrea Giammarchi < >>>>> [email protected]> wrote: >>>>> >>>>>> Like I've written before, if you need to return an array you can use >>>>>> map instead of forEach >>>>>> >>>>>> `arr.map(x => console.log(x) || x)` >>>>>> >>>>>> forEach has been like this since ever so while you wonder what kind >>>>>> of code would look like based on the fact forEach doesn't return >>>>>> anything, >>>>>> I actually wonder how come there are still people expecting forEach to >>>>>> return something. >>>>>> >>>>>> So, it would be a breaking change and actually it's not needed since >>>>>> you have map. >>>>>> >>>>>> If the new Array, and for debugging purpose, is not desired, use `var >>>>>> log = DEBUG ? x => console.log(x) || x : x => x` and abuse it as much as >>>>>> you like. >>>>>> >>>>>> Would any of this work? >>>>>> >>>>>> Regards >>>>>> >>>>>> >>>>>> >>>>>> On Fri, Oct 16, 2015 at 2:23 PM, Niloy Mondal < >>>>>> [email protected]> wrote: >>>>>> >>>>>>> > That'd be a compatibility break. >>>>>>> >>>>>>> Ugh... you mean people actually depend on `forEach` returning >>>>>>> `undefined` (which it always does) to do further task? >>>>>>> >>>>>>> I wonder what that kinda code would look like >.< >>>>>>> >>>>>>> On Fri, Oct 16, 2015 at 6:08 PM, Frankie Bagnardi < >>>>>>> [email protected]> wrote: >>>>>>> >>>>>>>> That'd be a compatibility break. >>>>>>>> >>>>>>>> If we end up getting :: though: >>>>>>>> >>>>>>>> ```js >>>>>>>> function logEach(){ >>>>>>>> this.forEach((x) => console.log(x)); >>>>>>>> return this; >>>>>>>> } >>>>>>>> >>>>>>>> >>>>>>>> const a = [1, 2, 3] >>>>>>>> .map(square) >>>>>>>> ::logEach() >>>>>>>> .map(plus1) >>>>>>>> .reduce(add); >>>>>>>> ``` >>>>>>>> >>>>>>>> You could make that a global variable so you can sprinkle it around >>>>>>>> your code in development. >>>>>>>> >>>>>>>> Having some developer tools in the language would be nice though. I >>>>>>>> don't even think console.log is in the spec. A global like >>>>>>>> Debug.logThis >>>>>>>> for example would be a more general ::-able. >>>>>>>> >>>>>>>> >>>>>>>> On Fri, Oct 16, 2015 at 5:32 AM, Andrea Giammarchi < >>>>>>>> [email protected]> wrote: >>>>>>>> >>>>>>>>> ```js >>>>>>>>> const a = [1, 2, 3] >>>>>>>>> .map(square) >>>>>>>>> .map(x => console.log(x) || x ) >>>>>>>>> .map(plus1) >>>>>>>>> .reduce(add); >>>>>>>>> ``` >>>>>>>>> >>>>>>>>> Regards >>>>>>>>> >>>>>>>>> >>>>>>>>> On Fri, Oct 16, 2015 at 10:13 AM, Niloy Mondal < >>>>>>>>> [email protected]> wrote: >>>>>>>>> >>>>>>>>>> Currently, `Array.prototype.forEach` returns `undefined`. It >>>>>>>>>> would be more >>>>>>>>>> useful if it returns the array itself. >>>>>>>>>> >>>>>>>>>> Say I have written some code like this... >>>>>>>>>> >>>>>>>>>> ```js >>>>>>>>>> const a = [1, 2, 3] >>>>>>>>>> .map(square) >>>>>>>>>> .map(plus1) >>>>>>>>>> .reduce(add); >>>>>>>>>> ``` >>>>>>>>>> >>>>>>>>>> For some reason, I am not getting the expected output. For >>>>>>>>>> debugging, I would >>>>>>>>>> like the print the values after each step. My first initial >>>>>>>>>> reaction is to >>>>>>>>>> put a `forEach` step in between and print the values like so... >>>>>>>>>> >>>>>>>>>> ```js >>>>>>>>>> const a = [1, 2, 3] >>>>>>>>>> .map(square) >>>>>>>>>> .forEach(x => console.log(x)) >>>>>>>>>> .map(plus1) >>>>>>>>>> .reduce(add); >>>>>>>>>> ``` >>>>>>>>>> >>>>>>>>>> Unfortunately, this does not work as `forEach` returns >>>>>>>>>> `undefined`. I now have >>>>>>>>>> to comment out all the code below it. Having the _plug and play_ >>>>>>>>>> behaviour for >>>>>>>>>> `forEach` would be very convenient. >>>>>>>>>> >>>>>>>>>> _______________________________________________ >>>>>>>>>> es-discuss mailing list >>>>>>>>>> [email protected] >>>>>>>>>> https://mail.mozilla.org/listinfo/es-discuss >>>>>>>>>> >>>>>>>>>> >>>>>>>>> >>>>>>>>> _______________________________________________ >>>>>>>>> es-discuss mailing list >>>>>>>>> [email protected] >>>>>>>>> https://mail.mozilla.org/listinfo/es-discuss >>>>>>>>> >>>>>>>>> >>>>>>>> >>>>>>> >>>>>> >>>>>> _______________________________________________ >>>>>> es-discuss mailing list >>>>>> [email protected] >>>>>> https://mail.mozilla.org/listinfo/es-discuss >>>>>> >>>>>> >>>>> >>>> >>>> _______________________________________________ >>>> es-discuss mailing list >>>> [email protected] >>>> https://mail.mozilla.org/listinfo/es-discuss >>>> >>>> >>> _______________________________________________ >>> es-discuss mailing list >>> [email protected] >>> https://mail.mozilla.org/listinfo/es-discuss >>> >> >
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