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

[Matthew Johnson]

Sent from my iPad

> On May 27, 2016, at 7:13 PM, Erica Sadun via swift-evolution <swift-evolution at swift.org> wrote:
> 
> 
>> On May 27, 2016, at 3:06 PM, Brandon Knope via swift-evolution <swift-evolution at swift.org> wrote:
>> 
>> Second, I have really gotten use to not needing to use semicolons, and this proposal seems to use/require them in very common situations.
>> 
>> After shedding the requirement of semicolons from ObjC…now we will have to use them a lot again?
>> 
>> 
>> Third, the format will look like this in most people’s code:
>> guard x == 0; let y = optional; y == 2 else {  //can the third bool condition even refer to y? Is it still in scope?
>> 	... 
>> }
>> (in the above example, y == 2 is related to the optional that precedes it. Now it looks like a distinct statement)
>> 
>> compared to
>> 
>> guard x == 0, let y = someOptional where y == 2 else { 
>> 	... 
>> }
>> 
>> 
>> To my eyes: the old way reads more naturally and looks less heavy. I think it keeps its expressiveness and also keeps it somewhat poetic.
> 
> This proposal serves the grammar, enabling it to simplify,  the compiler to avoid errors, and the developer to intermingle tests more naturally, as you would in processing JSON without having to nest or sequence separate guard statements. A main goal is differentiating the commas between conditions and in binding conditions, as you ask about below
> 
> I don't think it's practical to use a second braced scope:
> 
> guard {
>    condition
>    condition
>    condition
> } else {
>    leave scope
> }
> 
> This would be confusing to anyone doing conditional binding for use in the top level scope; the bindings would "escape" the braces. Using semicolons establishes a balance between separating different kinds of conditions and allowing comma-delineated multiple bindings.
> 
> Current state:
> 
> * Confusing, complicated, organically grown grammar
> * Inability to use independently standing Boolean assertions after the first (except for one outlier availability case)
> 
> Proposed state:
> 
> * Very simple grammar
> * Developer-directed ordering of binding, availability, Boolean assertions, cases, used in the order they're consumed
> * Slightly uglier
> 
> The cost for this is a separator between conditions

But we don't *have* to pay that cost if we handle them the same as other semicolons in the language.

> 
>> Also, can someone refer me to an example of this statement: "This proposal resolves this problem by retaining commas as separators within clauses (as used elsewhere in Swift) and introducing semicolons to separate distinct kinds of clauses (which aligns with the rest of the Swift language)”
> 
> guard let x = opt1, y = opt2, z = opt3; booleanAssertion else { }
> 
>> 
>> I rarely see any semicolons after the removal of C loops. So if someone could put me to where this is used elsewhere in Swift, please do!
> 
> Using semicolons brings conditions in-line with how semicolons are used as separators elsewhere in the Swift grammar.

Not really.  We can use a newline instead of the semicolon elsewhere.

> 
> -- Erica
> 
> 
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