duplicates:

• SR-6501 RangeReplaceableCollection default implementations cause infinite recursion

Issue Description:

The following compiles:

struct C : RangeReplaceableCollection {
    
    let startIndex = 0
    let endIndex = 0
    
    func index(after i: Int) -> Int { fatalError() }
    subscript(index: Int) -> String { return "" }
}

var c = C()
c.replaceSubrange(0 ..< 0, with: [])
print(c)

As the default implementation of replaceSubrange that takes an arbitrary RangeExpression and converts it to a Range<Index> is used to satisfy the replaceSubrange requirement – therefore leading to recursion when attempting to call, which isn't particularly intuitive.

Ideally, RangeReplaceableCollection should enforce that replaceSubrange is implemented.