On Fri, May 6, 2016, at 06:15 PM, Dave Abrahams via swift-evolution wrote:
>
> on Fri May 06 2016, Matthew Johnson <[email protected]> wrote:
>
> >> On May 6, 2016, at 7:30 PM, Dave Abrahams via swift-evolution
> >> <[email protected]> wrote:
> >>
> >>
> >> on Fri May 06 2016, Cole Campbell <[email protected]> wrote:
> >>
> >>> I don't know if it's considered too late at this point to rename
> >>> 'reduce', but
> >>> I'll add an enthusiastic +1 to renaming it to 'fold' and adding 'unfold'.
> >>> 'Fold'
> >>> is just as obvious a name as 'reduce', IMO (actually I even prefer
> >>> it).
> >>
> >> It's not, IMO. “Reduce” was chosen deliberately over “fold” because we
> >> think it is more in “common currency” among programmers, in no small
> >> part to the notice that MapReduce has gotten.
> >
> > I was guessing this was the rationale. But if it’s not too late and
> > “fold” solves the “unfold” naming problem maybe we that balances out
> > the equation.
>
> Personally, I'm not confident “unfold” would be considered to meet the
> utility bar, even if we changed the name of “reduce,” FWIW.
As I said to Chris in an off-list email, unfold() was actually the function
that I was the most excited about in the proposal, because it allows for a very
elegant solution to a variety of looping needs, especially now that we've
gotten rid of the C-style for loops. One example of its use is something like
// Iterate over self.view and all its ancestor views.
for view in unfold(self.view, applying: { $0.superview }) {
// ...
}
In fact, just today I hit this exact issue and wished I had unfold(). This same
pattern works for any case where an object has a property of the same type and
you want to walk the entire chain, such as
UIViewController.presentingViewController, or
NSError.userInfo[NSUnderlyingErrorKey].
It also integrates very nicely with the other sequence methods, including
drop(while:) and prefix(while:). For example:
// Iterate over someView and all its ancestors, stopping at self.view
for view in unfold(someView, applying: { $0.superview }).prefix(while: { $0
!== self.view }) {
// ...
}
Incidentally, I tried writing up an example of using the stateful version to
reimplement zip(), but it ended up being a good argument in favor of the
suggestion someone (maybe you?) had for turning the state into an inout
parameter.
-Kevin Ballard
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