Butcher protocol for head/tail of Array

README.md

butcher.swift

head/tail implementation using protocol

butcher.python.swift

another implementation inspired from python

// Swift // python
var arr = [1,2,3] // arr = [1,2,3]
arr[1..(-1)] // arr[1:-1]
arr[1..(-2)] // arr[1:-2]

butcher.python.swift

@infix func .. (lhs: Int, rhs: Int) -> (Int, Int) {
    return (lhs, rhs)
}

extension Array {
    subscript(range: (Int, Int)) -> [T] {
        var (start, end) = range
        end = end < 0 ? self.count + end : end
        return Array(self[start...end])
    }
    
    var head: T {
        get { return self[0] }
    }
    var tail: [T] {
        get { return self[1..(-1)] }
    }
    
}

butcher.swift

protocol Butcher {
    typealias T
    var head: T { get }
    var tail: Array<T> { get }
}

extension Array:Butcher {
    typealias Foo = T
    
    var head: T {
    // non-optional for optimization
    get { return self[0] }
    }
    var tail: Array<T> {
    get {
        return self.count > 1 ? Array(self[1..<self.count]) : []
    }
    }
}


var char = ["a", "b", "c", "d"]
println(char.head)
println(char.tail)

var arr = [1]
println(arr.head)
println(arr.tail)

var arr2:Array<Int> = []
arr2.head // error occured