[swift-evolution] Proposal Sketch: simplify optional unwrapping syntax

[Sean Heber]

I would not have “without” - only “with”.  If you wanted to put it into a guard, I’d go with guard-with. If the *only* intent of the “with" keyword was to unwrap-in-place (basically), then I’d imagine it would *only* work inside an if or guard and not stand on its own. If it was combined with Erica’s proposal, I think it could stand on its own, though.

> with x = a?.b.c?.d where !x.isEmpty, y = something(x) {
>    // the scope cannot reference to both (x and y) now
> }


If you’re declaring “x” for the first time, you’d have to have a let/var in there.

with let x = <potentially optional expression>, y = <another optional expression> where <cond> {}

l8r
Sean


> On Dec 11, 2015, at 10:52 AM, Marc Knaup <marc at knaup.koeln> wrote:
> 
> So guard let x = x would become without x or guard with x else? :)
> 
> Seems weird to have two control statements which do almost the same thing:
> 	• if (for any conditions) + with (for a subset of things doable with if)
> 	• guard (for any conditions) + without (for a subset of things doable with guard)
> Also with/without would have to carry over the where clause which basically is a if too.
> 
> And with multiple assignments Erica's proposal would not work anymore.
> 
> As in my previous example (made a bit larger to showcase where):
> 
> 
> 
> Btw. there was a rather short discussion in Apple Developer Forums some time ago too.
> 
> On Fri, Dec 11, 2015 at 5:40 PM, Sean Heber <sean at fifthace.com> wrote:
> This has come up a few times. I’ve thrown my 2cents into a variant of “with” to solve this rather than messing with the meaning of if-let:
> 
> For example:
> 
> var x: MyType?
> 
> with x {
>   x.someFunction()              // okay - this entire block is skipped if “x” is nil anyway
> }
> x.someFunction()                // not okay as-is since x is optional
> 
> 
> Using the definition  of “with” from Erica’s Method Cascading proposal https://gist.github.com/erica/6794d48d917e2084d6ed, you could even drop the variable reference itself from inside the block body:
> 
> with x {
>   someFunction()                // would call “someFunction()” on “x”
> }
> 
> 
> And I’d additionally propose that if you wanted to replace if-let-else, you could potentially do this:
> 
> if with x {
>   // x is known non-nil
> } else {
>   // x is known to be nil
> }
> // x is optional and nil-ness is unknown
> 
> 
> l8r
> Sean
> 
> 
> > On Dec 11, 2015, at 10:28 AM, Marc Knaup via swift-evolution <swift-evolution at swift.org> wrote:
> >
> > One problem with dropping if/guard let is something like this:
> >
> > if let x = a?.b.c?.d, y = something(x) {
> >    …
> > }
> >
> > would then have to become this:
> >
> > let x = a?.b.c?.d
> > if x != nil {
> >    let y = something(x)
> >    if y != nil {
> >        …
> >    }
> > }
> >
> > I'm fine with
> >    if let x
> > as a shortcut for
> >    if let x = x
> >
> > It just reads a bit weird - like declaring an immutable variable with no type and no value.
> >
> >
> > On Fri, Dec 11, 2015 at 5:19 PM, Jeff Kelley via swift-evolution <swift-evolution at swift.org> wrote:
> > I’ve had similar ideas to this. Instead of ditching the if let syntax altogether, another approach would be to use the existing name if no new name is given, so that this code:
> >
> >       if let foo = foo { /* use foo */ }
> >
> > could become this code:
> >
> >       if let foo { /* use foo */ }
> >
> > In both cases, foo is non-optional inside the braces. If you gave it another name with the if let syntax, that would work as it does today.
> >
> >
> > Jeff Kelley
> >
> > SlaunchaMan at gmail.com | @SlaunchaMan | jeffkelley.org
> >
> >> On Dec 11, 2015, at 11:11 AM, Daniel Hooper via swift-evolution <swift-evolution at swift.org> wrote:
> >>
> >> A very common pattern in swift code is to "guard let" or "if let" optionals  - this works by creating a new non-optional variable to be used by future code. Often, the new variable is given the same name as the original optional variable, creating a shadow variable. This approach leads to odd looking code like this:
> >>
> >> if let nearestX = nearestX { closest = nearestX }
> >> guard let layer = layer else { continue }
> >> // use layer
> >>
> >> At a glance, and to Swift newcomers, this code looks completely non-sensical. It's also verbose for simply ensuring the variable is non-nil.
> >>
> >> The solution:
> >> Swift should generate unwrapped shadow variables after nil checking. The compiler would treat the below code as if it had created an unwrapped shadow variable.
> >>
> >> if nearestX != nil { closest = nearestX } // notice that nearestX isn't force unwrapped
> >> guard layer != nil else { continue }
> >> // use layer, without force unwrapping
> >>
> >> Why force unwrapping isn't a good alternative:
> >> You might suggest force unwrapping variables when they're inside an if or after a guard that checks for nil. While this does allow for the "layer = nil" syntax, it results in code that is less resilient to change. Imagine that this code was written:
> >>
> >> {code:java}
> >> if layer != nil {
> >> // lots of code before //
> >> layer!.backgroundColor = newColor
> >> // lots of code after //
> >> }
> >> {code}
> >>
> >> And much later, you need to use some of the the code in the if body elsewhere, so you copy and paste a huge chunk of it. You likely won't notice the force unwrap, and unless you're lucky, you probably didn't paste it into an if that checked layer for nil. So you get a crash. Because of this, it's important we make safe optional unwrapping as easy and sensical as possible, and minimize the situations that you would need to force unwrap.
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> >
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