pofat

import Foundation

// struct for printing out instance address
struct MemoryAddress<T>: CustomStringConvertible {

    let intValue: Int
    var description: String {
        let length = 2 + 2 * MemoryLayout<UnsafeRawPointer>.size
        return String(format: "%0\(length)p", intValue)
    }

pofat

// 會帶真實型別進去
func doSomething<T: MyPotocol>(_ arg: T) { }
// 有 existentail container
func doSomething(_ arg: MyProtofcol) { }

pofat

/*
 * Standard library 有個 protocol `CustomStringConvertible`，需要實作 `description: String` 來將一個物件轉化成 description string
 * 但是若你對同一個物件想要有兩種描述方式，比如
 * 想要用 JSON 的方式印出來 model 的所有 property，且希望有的時候是 pretty printed 有的時候是 sorted key 怎麼辦？
 * 你會需要有兩個物件來遵守 CustomStringConvertible，因為一個 protocol 在一個物件裡只能有一種實作
 * 然而用 generic struct 的話就能做到這件事
 * 下面的實例中你可以宣告兩個不同的 instance ，`prettyPrintedDescribing` 和 `sortedKeyDescribing`
 * 想用哪個就用哪個，方便多了，也讓 compiler 有更多參與最佳化的空間
 *
 */

pofat

import Foundation
import RxSwift

// MARK: Model
struct User: Decodable {
    let id: Int
    let name: String
}

let usersDecode: (Data) -> [User]? = { data in

pofat

// From:
protocol Drawable {
    func draw()
}

// To:
struct Drawing<Shape> {
    var draw: (Shape) -> ()
}

pofat

struct ExistentialContainer {
    var valueBuffer: (Int, Int, Int)
    var vwt: UnsafePointer<ValueWitness>
    var pwt: UnsafePointer<ProtocolWitness>
}

struct ProtocolWitness {
    var descriptor: ProtocolConformanceDescriptor
    var draw: FunctionRef
}

pofat

protocol Drawable {
    func draw()
}

struct Point: Drawable {
    var x: Int
    var y: Int
    
    func draw() {
        print("Draw a point at (\(x), \(y))")

pofat

import Foundation
import RxSwift

// Requests 
enum HTTPMethod: String {
    case POST, GET
}

// Define what a request is
protocol Request {

pofat

struct ExistentialContainer {
    var valueBuffer: (Int, Int, Int)
    var vwt: UnsafePointer<ValueWitness>
    var pwt: UnsafePointer<ProtocolWitness>
}

protocol Fooable {
    func foo()
}

pofat

protocol MyProcotol {}

struct MyStruct {
  let x = 1
  let y = 2
}
// What's the difference of following two?
let existentialContainer: MyProtocol = MyStruct()
let structInstance = MyStruct()