Details
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Type:
Bug
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Status: Open
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Priority:
Medium
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Resolution: Unresolved
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Component/s: None
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Labels:None
Description
This program compiles as expected:
protocol VectorIndex {}
protocol Vector {
associatedtype Element
associatedtype Index: VectorIndex
subscript(index: Index) -> Element { get set }
init(_ indexToElementMapping: (Index) -> Element)
}
// Some methods for square matrices:
extension Vector where
Self.Element: Vector,
Self.Index == Self.Element.Index,
Self.Element.Element: BinaryFloatingPoint
{
func row(_ index: Index) -> Element { self[index] }
func column(_ index: Index) -> Element { Element { self[$0][index] } }
}
But note that if we make VectorIndex inherit/refine CaseIterable, like so:
protocol VectorIndex: CaseIterable {}
The program will no longer compile, because:
error: cannot convert value of type 'Self.Element.Index' (associated type of protocol 'Vector') to expected argument type 'Self.Index' (associated type of protocol 'Vector')
ie, it seems like the constraint Self.Index == Self.Element.Index is now being ignored.
