[swift-evolution] guard let x = x

[Sean Heber]

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.

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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