IndexDifference.swift

extension Collection where Iterator.Element: Equatable {
    
    /// Computes the indices of different elements between two collections. This is useful for updating table views
    /// with row deletions and insertion
    /// - Parameter other: the collection to compute the index difference
    /// - Returns: a tuple with indices to delete and insert on `self` to create a collection equivalent to `other`
    /// - Discussion: This algorithm does not work for collections with duplicate elements.
    public func indexDifference(with other: Self) -> (deleted: [Index], inserted: [Index]) {
        var (deleted, inserted): ([Index], [Index]) = ([], [])
        
        for (offset, element) in self.enumerated() where !other.contains(element) {
            let i = index(startIndex, offsetBy: numericCast(offset))
            deleted.append(i)
        }
        
        for (offset, element) in other.enumerated() where !self.contains(element) {
            let i = index(startIndex, offsetBy: numericCast(offset))
            inserted.append(i)
        }
        
        return (deleted, inserted)
    }
}