Comparing two arrays for changes

Change.swift

enum Change {
    case Insert(at: Int)
    case Delete(at: Int)
    case Move(from: Int, to: Int)
}

extension Change: Printable {
    var description: String {
        switch self {
        case .Insert(let at):
            return "(Insert \(at))"
        case .Delete(let at):
            return "(Delete \(at))"
        case .Move(let from, let to):
            return "(Move \(from)->\(to))"
        }
    }
}

func ExtractChanges<T: Hashable>(source: [T], dest: [T]) -> [Change] {
    var changes = [Change]()
    
    var sourceIndex = [T: Int]()
    for (i,v) in enumerate(source) {
        sourceIndex[v] = i
    }
    
    for (i,v) in enumerate(dest) {
        if let prevIndex = sourceIndex[v] {
            if prevIndex != i {
                changes.append( .Move(from: prevIndex, to: i) )
            } else {
                // no change
            }
            sourceIndex.removeValueForKey(v)
        } else {
            changes.append( .Insert(at: i) )
        }
    }
    
    for i in sourceIndex.values {
        changes.append( .Delete(at: i) )
    }
    
    return changes
}