[swift-evolution] Proposal: Optional Binding Shorthand Syntax

[Zef Houssney]

Interesting thoughts! And thanks for the consideration Chris. Just a couple more thoughts and I’ll drop this :)

Chris, I love the way you put this:

> Since code is read more often than it is written, the real goal behind Swift is to let you write “more readable code” by eliminating boilerplate and other noise.

In my view, this proposal is aligned with that goal and it’s as much about readability as anything. I find this first example so much more readable at a glance, and I consider the duplicate names and equals sign to be in the boilerplate/noise category:

if let thing, otherThing, moreThings where thing > 0 { }
if let thing = thing, otherThing = otherThing, moreThings = moreThings where thing > 0 { }


Kevin, in regard to this:

> Furthermore, to anyone not already familiar with the proposed rule, `if let foo {` is meaningless


I agree with David in that the existing syntax is already at the point where your statement is also true. There is nothing in the current syntax that indicates that you are unwrapping the optional. It’s only through learning or familiarity with other languages that one understands it. The = indicates assignment, but the unwrapping is learned and specific to that context. The jump to this seems super easy to grok.

Also my point isn’t that it’s doing the same thing technically, but that it’s a similar concept — assigning to a constant with the value derived implicitly by the context instead of directly through ‘=‘.

The idea of another keyword like “when” also seems plausible to me, though it’s a much more drastic change.




> On Dec 3, 2015, at 8:13 PM, Sean Heber <sean at fifthace.com> wrote:
> 
> What about lifting the whole concept out of "if" or "guard" and making a new construct that directly communicates the intent?
> 
> For example:
> 
> when foo { ... }
> 
> Which could be combined with "where" to generate an if-like construct:
> 
> when foo where foo.isSomething { ... }
> 
> Inside the code block, you can access foo directly and it isn't shadowed - so if it was a var, it is mutable, etc.
> 
> l8r
> Sean
> 
> 
> On Dec 3, 2015, at 8:25 PM, David Waite <david at alkaline-solutions.com <mailto:david at alkaline-solutions.com>> wrote:
> 
>> I might argue that if let is already an odd case; people often read it equivalent to "if (let x=x)”, but “let x=x” has completely different behavior outside the context of an if let statement (I in fact had to try it before I realized it does, in fact, work). Obviously, 'let x=x’ on its own could not have the same behavior.
>> 
>> In that spirit, I propose an alternative feature:
>> 
>> if foo? { … }
>> 
>> where the variable is not shadowed by a copy - instead, inside the block it behaves as an implicit unwrapped optional, including keeping any mutability.
>> 
>> so for example:
>> 
>>  func foo(x:Int?) { 
>>      if var x = x { // var so it can be assigned
>>          x++ 
>>      } 
>>      print(x) 
>>  } 
>> 
>> foo(1) // => 1, updating the aliased x does not do anything
>> 
>> # working code in Swift 1.2
>>  func bar(x:Int?) { 
>>      var y=x 
>>      if let x=x { 
>>          y=x+1 
>>      } 
>>      print(y) 
>>  } 
>> bar(1) # => Optional(2)
>> 
>> # proposed
>> func proposed(x:Int?) {
>>      var y = x // since swift 3 won't have var function arguments
>>      if y? { // var so it can be assigned
>>          y++ 
>>      } 
>>      print(y) 
>>  } 
>> 
>> proposed(1) // => Optional(2)
>> 
>> -DW
>> 
>>> On Dec 3, 2015, at 3:42 PM, Chris Lattner <clattner at apple.com <mailto:clattner at apple.com>> wrote:
>>> 
>>> 
>>> “if let foo {“ is a frequently proposed extension to the syntax, but it is not one that we’re likely to ever add.
>>> 
>>> I agree that this is a common pattern, and it would allow you to “write less code”, but that isn’t the goal of Swift.  Since code is read more often than it is written, the real goal behind Swift is to let you write “more readable code” by eliminating boilerplate and other noise. 
>>> 
>>> Reducing syntax isn’t itself a goal, particularly if the result could/would be confusing for someone who has to read and maintain your code later.
>>> 
>>> -Chris
>> 
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