[swift-evolution] guard let x = x

[Hooman Mehr]

> On Nov 2, 2016, at 2:02 PM, Matthew Johnson via swift-evolution <swift-evolution at swift.org> wrote:
>> On Nov 2, 2016, at 3:47 PM, Sean Heber via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> 
>> For what it’s worth, I concur. I think type narrowing makes it feel more like the language is actually doing some work *for* me rather than me having to babysit the language with some new syntax or keyword.
> 
> I’ve been staying out of the discussion because it doesn’t seem particularly relevant to Swift 4 phase 1, but +1.  Type narrowing is by far the most general and scalable solution which could be applied in other ways in the future.
> 

Same as me, I was staying out as well. 
+1 for type narrowing instead of the original proposal. Thank you Haravikk for bringing this up.

>> 
>> l8r
>> Sean
>> 
>>> On Nov 2, 2016, at 3:25 PM, Haravikk via swift-evolution <swift-evolution at swift.org> wrote:
>>> 
>>> I still think that type narrowing is the right way to handle this like so:
>>> 
>>> 	if x != nil {
>>> 		// x is definitely not nil inside this block (implicitly unwrapped)
>>> 	} // x remains optional outside of it
>>> 
>>> 	if (x != nil) || (x == y) {
>>> 		// if y's type is non-optional, then x is definitely not nil inside this block also
>>> 		// i.e- if all conditions narrow to the same result, the type is narrowed inside the block
>>> 	}
>>> 
>>> 	if x is Foo {
>>> 		x.someMethodSpecificToFoo()
>>> 	}
>>> 
>>> Personally I'm very much against the use of shadowing in the first place, and never use it myself. I tend to precede unwrapped value with "this" like so:
>>> 
>>> 	if let thisFoo = foo {
>>> 		// Do something with thisFoo
>>> 	}
>>> 
>>> I know it's maybe down to personal preference but I'd prefer to discourage shadowing entirely, and focus on type-narrowing, as it's a much more natural, and more generally useful, way to handle this "problem", as it doesn't actually require a specific syntax at all; if your condition narrows the type, then you can use the variable as whatever it is known to be.
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