Unary-indexed Collection (ported from Swift Sandbox)

unary-indexed-collection.swift

//  Write some awesome Swift code, or import libraries like "Foundation",
//  "Dispatch", or "Glibc"

import Foundation

struct SampleCollection: LazyCollectionProtocol, RandomAccessCollection {
    typealias Indices = DefaultRandomAccessIndices<SampleCollection>

    let xs = ["a", "b", "c"]
    
    var startIndex: String {
        return ""
    }
    
    var endIndex: String {
        return "xxx"
    }
    
    func index(after i: String) -> String {
        return i + "x"
    }
    
    func index(before i: String) -> String {
        return String((0..<(i.count-1)).map{ _ in "x" })
    }
    
    subscript(i: String) -> String {
        return xs[i.count]
    }
}

/*struct LazyShuffleRandomAccessCollection<Base: RandomAccessCollection>: LazyCollectionProtocol {
    
    /*typealias Index = Base.Index
    typealias IndexDistance = Base.IndexDistance
    typealias SubSequence = Base.SubSequence
    typealias Indices = Base.Indices
    typealias Iterator = Base.Iterator*/
    
    let base: RandomAccessCollection
    
    var startIndex: Index {
        self.base.startIndex
    }
    
    var endIndex: Index {
        self.base.endIndex
    }
    
    func makeIterator() -> Iterator {
        return self.base.makeIterator()
    }
    
    func index(after: IndexDistance) -> Index {
        return self.base.index(after: after)
    }
    
    /*subscript(bounds: Range<Index>) -> SubSequence {
        return self.base[bounds]
    }*/
} */


let x = [1,2,3]

let y = sequence(first: 0, next: { i in i + 1 }).lazy.map{ x in x + 1 }.filter{ x in x % 2 == 0 }

print(SampleCollection().map{ x in x + "!" }["xx"])