OK, but your example wouldn't be acceptable in JavaScript, because it's inconsistent with how `for(;;)` does initialization before the first `;`, which is before iteration.
That's why I was saying that initializers-as-expressions simplifies doing things like that, despite the other concerns. On Mon, 26 Mar 2018 at 12:18 Isiah Meadows <[email protected]> wrote: > Maybe this analogue to the `for (const ... of ...)`: > > ```js > function keyList(map) { > const list = new Array(map.size) > const iter = map.keys() > > while (const {done, value} = iter.next(); !done) { > list.push(value) > } > > return list > } > ``` > > But in general, the more I've thought about it, the more I've noticed > it doesn't generalize well past the C-style `for` loop and I find > myself getting ready to reinvent an awkward minor variant of it > repeatedly. And without anything to the tune of pattern matching > (which Rust has) or a `loop`/`recur`-like `while`-ish loop (which is > what Clojure uses instead), it just seems pointless. > > ----- > > Isiah Meadows > [email protected] > > Looking for web consulting? Or a new website? > Send me an email and we can get started. > www.isiahmeadows.com > > > On Mon, Mar 26, 2018 at 2:33 AM, Naveen Chawla <[email protected]> > wrote: > > I don't get it. Please give an example of the per-iteration > initialization > > in the while loop... (the for-loop version before `;` does it before > > iteration, not per-iteration) > > > > On Mon, 26 Mar 2018 at 07:20 Isiah Meadows <[email protected]> > wrote: > >> > >> As a counterpoint, Rust and Swift are the opposite: it's only defined > >> in the consequent branch, not the alternate. So it could go both ways. > >> > >> But if a value is useful in both branches, I'd prefer to just define > >> the variable in a separate statement, to clarify that it's useful in > >> both branches (explicit > implicit). To take your example, I'd prefer > >> instead to do this: > >> > >> ```js > >> let foo = getFoo() > >> > >> if (foo.isReady()) { > >> foo.start() > >> } else { > >> foo.wait() > >> } > >> ``` > >> ----- > >> > >> Isiah Meadows > >> [email protected] > >> > >> Looking for web consulting? Or a new website? > >> Send me an email and we can get started. > >> www.isiahmeadows.com > >> > >> > >> On Sun, Mar 25, 2018 at 5:42 AM, Maël Nison <[email protected]> > wrote: > >> > C++ defines it as being available in both branches, I think we try to > >> > share > >> > the same behavior. Keep in mind that it will useful when the check is > on > >> > something different than existence : > >> > > >> > if (let foo = getFoo() ; foo.isReady()) > >> > foo.start(); > >> > else > >> > foo.wait(); > >> > > >> > On Wed, Mar 21, 2018, 10:27 PM Isiah Meadows <[email protected]> > >> > wrote: > >> >> > >> >> My implication was that it'd only be available in the `if` (if > >> >> declared with `let`/`const`). > >> >> ----- > >> >> > >> >> Isiah Meadows > >> >> [email protected] > >> >> > >> >> Looking for web consulting? Or a new website? > >> >> Send me an email and we can get started. > >> >> www.isiahmeadows.com > >> >> > >> >> > >> >> On Wed, Mar 21, 2018 at 6:25 PM, Sebastian Malton > >> >> <[email protected]> > >> >> wrote: > >> >> > Sorry if I missed a message but would such an initialization be > only > >> >> > available in the first `if` block or also in the subsequent `else > if` > >> >> > and > >> >> > `else` blocks? > >> >> > > >> >> > Sebastian Malton > >> >> > > >> >> > > >> >> > Original Message > >> >> > From: [email protected] > >> >> > Sent: March 21, 2018 6:18 PM > >> >> > To: [email protected] > >> >> > Cc: [email protected]; [email protected] > >> >> > Subject: Re: Proposal: if variable initialization > >> >> > > >> >> > I'm personally very much *for* this `if (var ...; cond) { ... }` > >> >> > syntax. I couldn't tell you how many times I would've liked > something > >> >> > to that effect, since that's probably one of my biggest areas of > >> >> > boilerplate. > >> >> > > >> >> > I would also be in favor of `if (var ...) { ... }` as a shorthand > >> >> > that > >> >> > guards `!= null` the expression result (pre-match), since that's > >> >> > about > >> >> > 90% of my use cases for it. There *is* a potential area of > ambiguity > >> >> > in sloppy for `if ( let [ x ] = y )`, since that would be currently > >> >> > parsed as `var tmp = y; let[x] = tmp; if (tmp) { ... }`, but I > doubt > >> >> > breaking that would be of much web compat risk. (A similar > ambiguity > >> >> > existed with `for (let [`, but that break didn't cause many > issues.) > >> >> > ----- > >> >> > > >> >> > Isiah Meadows > >> >> > [email protected] > >> >> > > >> >> > Looking for web consulting? Or a new website? > >> >> > Send me an email and we can get started. > >> >> > www.isiahmeadows.com > >> >> > > >> >> > > >> >> > On Wed, Mar 21, 2018 at 2:47 PM, Mike Samuel <[email protected] > > > >> >> > wrote: > >> >> >> > >> >> >> > >> >> >> On Wed, Mar 21, 2018 at 1:27 PM, Sebastian Malton > >> >> >> <[email protected]> > >> >> >> wrote: > >> >> >>> > >> >> >>> Because block-level scoping is a very good way to avoid certain > >> >> >>> bugs > >> >> >>> and > >> >> >>> is easier to reason about. Especially when considering project > >> >> >>> successors. > >> >> >> > >> >> >> > >> >> >> +1. function-scoped variables in loop bodies caused tons of bugs > >> >> >> before > >> >> >> let-scoped variables and were a main motivating case. > >> >> >> > >> >> >> var i; > >> >> >> for (i = 0; i < arr.length; ++i) { > >> >> >> f(function () { /* Do something with */ arr[i]; }); > >> >> >> } > >> >> >> > >> >> >> vs > >> >> >> > >> >> >> for (let i = 0; i < arr.length; ++i) { > >> >> >> f(function () { /* Do something with */ arr[i]; }); > >> >> >> } > >> >> >> > >> >> >> Yes, linters got pretty good at finding uses of closed-over > >> >> >> variables > >> >> >> modified in a loop, but the workarounds were not ideal. > >> >> >> > >> >> >> var i; > >> >> >> for (i = 0; i < arr.length; ++i) { > >> >> >> f(function (i) { return function () { /* Do something with */ > >> >> >> arr[i]; > >> >> >> } > >> >> >> }(i)); > >> >> >> } > >> >> >> > >> >> >> Block scoping is just better for code that uses loops, variables, > >> >> >> and > >> >> >> function expressions. > >> >> >> > >> >> >> > >> >> >> _______________________________________________ > >> >> >> 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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