For a Swift SequenceType, return a lazy sequence of elements that conform to a specified type

asLazySequence.swift

import Foundation

extension SequenceType {
    /// Return a lazy sequence of elements of this sequence that are of type T
    func asLazySequence<T>() -> LazyMapSequence<LazyFilterSequence<Self>, T> {
        return self.lazy.filter{ $0 is T }.map{ $0 as! T }
    }
    
    /// Return a lazy sequence of the elements that are NSDictionary instances
    func asLazyNSDictionarySequence()
        -> LazyMapSequence<LazyFilterSequence<Self>, NSDictionary>
    {
        return asLazySequence()
    }
}