[swift-users] Range subscript is ambiguous

[Chris Lattner]

On May 16, 2016, at 10:09 AM, Joe Groff via swift-users <swift-users at swift.org> wrote:
> 
>> The oddity is that if I change the assignment to this
>> 
>>   var y : [Int] = Array(a[0..<n])
>> 
>> then the compiler is happy.
>> 
>> Shouldn’t it be able to do any necessary type inference from the fact that the expression is in a context where an array is required?
> 
> The error message is misleading (if you have time, we'd appreciate a bug report!). What's really going on is that a[0..<n] produces an ArraySlice<T>, not an Array<T>, in order to share memory with the underlying array. The type doesn't match in your assignment. If `x` is just temporary, I'd recommend leaving the type annotation out, since `var x = a[0..<n]` should just work.

FWIW, master produces the error:

test.swift:2:27: error: cannot subscript a value of type '[Int]' with an index of type 'CountableRange<Int>'
         var x : [Int] = a[0..<n]
                          ^
test.swift:2:27: note: overloads for 'subscript' exist with these partially matching parameter lists: (Int), (Range<Int>), (Range<Self.Index>), (ClosedRange<Self.Index>), (CountableClosedRange<Self.Index>)
         var x : [Int] = a[0..<n]
                          ^

-Chris