[swift-evolution] [swift-evolution-announce] [Review] SE-0099: Restructuring Condition Clauses

[David Hart]

Yet another alternative: would it be possible to disallow commas as variable declaration separators and use them for condition clause separators again:

let a = 4, b = 8 // becomes illegal and requires to separate them on two lines

if a > 4, let c = foo(), let d = bar(), c != d { // now comma is not ambiguous anymore
}

David.

> On 28 May 2016, at 02:30, Erica Sadun via swift-evolution <swift-evolution at swift.org> wrote:
> 
>> 
>> On May 27, 2016, at 6:26 PM, Brent Royal-Gordon <brent at architechies.com> wrote:
>> 
>>> guard
>>> x == 0 && a == b && c == d &&
>>> let y = optional, w = optional2, v = optional 3 &&
>>> z == 2
>>> else { ... }
>>> 
>>> Figuring out where to break the first line into expression and into condition (after the `d`) could be very challenging to the compiler.
>> 
>> I'm not sure it is. `let` and `case` are not valid in an expression, so an `&&` followed by `let` or `case` must be joining clauses. On the other side of things, Swift's `&&` doesn't ever produce an optional, so if we're parsing an expression at the top level of an if-let, an `&&` must indicate the end of the clause. An if-case *could* theoretically include an `&&`, but pattern matching against a boolean value seems like a fairly useless thing to do in a context that's specifically intended to test booleans.
> 
> Let me answer in another way that speaks to my background which isn't in compiler theory: The use of && may produce cognitive overload between the use in Boolean assertions and the use in separating condition clauses.
> 
> -- E
> 
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