MemoryLayout<Int>.size // return 8 (on 64-bit)
MemoryLayout<Int>.alignment // return 8 (on 64-bit)
MemoryLayout<Int>.stride // return 8 (on 64-bit)
MemoryLayout<Int16>.size // return 2
MemoryLayout<Int16>.alignment // return 2
MemoryLayout<Int16>.stride // return 2
MemoryLayout<Bool>.size // return 2
MemoryLayout<Bool>.alignment // return 2
MemoryLayout<Bool>.stride // return 2
MemoryLayout<Float>.size // return 4
MemoryLayout<Float>.size // return 4
MemoryLayout<Float>.alignment // return 4
MemoryLayout<Double>.stride // return 8
MemoryLayout<Double>.alignment // return 8
MemoryLayout<Double>.stride // return 8

struct EmptyStruct {}
MemoryLayout<EmptyStruct>.size // returns 0
MemoryLayout<EmptyStruct>.alignment // returns 1
MemoryLayout<EmptyStruct>.stride // returns 1
struct SampleStruct {
 let number: UInt32
 let flag: Bool
}
MemoryLayout<SampleStruct>.size // returns 5
MemoryLayout<SampleStruct>.alignment // returns 4
MemoryLayout<SampleStruct>.stride // returns 8

class EmptyClass {}
MemoryLayout<EmptyClass>.size // returns 8 (on 64-bit)
MemoryLayout<EmptyClass>.alignment // returns 8 (on 64-bit)
MemoryLayout<EmptyClass>.stride // returns 8 (on 64-bit)
class SampleClass {
 let number: Int64 = 0
 let flag: Bool = false
}
MemoryLayout<SampleClass>.size // returns 8 (on 64-bit)
MemoryLayout<SampleClass>.aligment // returns 8 (on 64-bit)
MemoryLayout<SampleClass>.stride // returns 8 (on 64-bit)

// 1
let count = 2
let stride = MemoryLayout<Int>.stride
let alignment = MemoryLayout<Int>.alignment
let byteCount = stride * count
 
// 2
do {
 print("Raw pointers")
 
 // 3
 let pointer = UnsafeMutableRawPointer.allocate(bytes: byteCount, alignedTo: alignment)
 // 4
 defer {
 pointer.deallocate(bytes: byteCount, alignedTo: alignment)
 }
 
 // 5
 pointer.storeBytes(of: 42, as: Int.self)
 pointer.advanced(by: stride).storeBytes(of: 6, as: Int.self)
 pointer.load(as: Int.self)
 pointer.advanced(by: stride).load(as: Int.self)
 
 // 6
 let bufferPointer = UnsafeRawBufferPointer(start: pointer, count: byteCount)
 for (index, byte) in bufferPointer.enumerated() {
 print("byte \(index): \(byte)")
 }
}

do {
 print("Typed pointers")
 
 let pointer = UnsafeMutablePointer<Int>.allocate(capacity: count)
 pointer.initialize(to: 0, count: count)
 defer {
 pointer.deinitialize(count: count)
 pointer.deallocate(capacity: count)
 }
 
 pointer.pointee = 42
 pointer.advanced(by: 1).pointee = 6
 pointer.pointee
 pointer.advanced(by: 1).pointee
 
 let bufferPointer = UnsafeBufferPointer(start: pointer, count: count)
 for (index, value) in bufferPointer.enumerated() {
 print("value \(index): \(value)")
 }
}

do {
 print("Converting raw pointers to typed pointers")
 
 let rawPointer = UnsafeMutableRawPointer.allocate(bytes: byteCount, alignedTo: alignment)
 defer {
 rawPointer.deallocate(bytes: byteCount, alignedTo: alignment)
 }
 
 let typedPointer = rawPointer.bindMemory(to: Int.self, capacity: count)
 typedPointer.initialize(to: 0, count: count)
 defer {
 typedPointer.deinitialize(count: count)
 }
 
 typedPointer.pointee = 42
 typedPointer.advanced(by: 1).pointee = 6
 typedPointer.pointee
 typedPointer.advanced(by: 1).pointee
 
 let bufferPointer = UnsafeBufferPointer(start: typedPointer, count: count)
 for (index, value) in bufferPointer.enumerated() {
 print("value \(index): \(value)")
 }
}

do {
 print("Getting the bytes of an instance")
 
 var sampleStruct = SampleStruct(number: 25, flag: true)
 
 withUnsafeBytes(of: &sampleStruct) { bytes in
 for byte in bytes {
 print(byte)
 }
 }
}

 // Rule #1
do {
 print("1. Don't return the pointer from withUnsafeBytes!")
 
 var sampleStruct = SampleStruct(number: 25, flag: true)
 
 let bytes = withUnsafeBytes(of: &sampleStruct) { bytes in
 return bytes // strange bugs here we come ☠️☠️☠️
 }
 
 print("Horse is out of the barn!", bytes) /// undefined !!!
}

// Rule #2
do {
 print("2. Only bind to one type at a time!")
 
 let count = 3
 let stride = MemoryLayout<Int16>.stride
 let alignment = MemoryLayout<Int16>.alignment
 let byteCount = count * stride
 
 let pointer = UnsafeMutableRawPointer.allocate(bytes: byteCount, alignedTo: alignment)
 
 let typedPointer1 = pointer.bindMemory(to: UInt16.self, capacity: count)
 
 // Breakin' the Law... Breakin' the Law (Undefined behavior)
 let typedPointer2 = pointer.bindMemory(to: Bool.self, capacity: count * 2)
 
 // If you must, do it this way:
 typedPointer1.withMemoryRebound(to: Bool.self, capacity: count * 2) {
 (boolPointer: UnsafeMutablePointer<Bool>) in
 print(boolPointer.pointee) // See Rule #1, don't return the pointer
 }
}
**絕對(duì)不要**讓一個(gè)內(nèi)存同時(shí)綁定兩個(gè)不同的類型。如果你需要臨時(shí)這么做，可以使用 `withMemoryRebound(to:capacity:)` 來對(duì)內(nèi)存進(jìn)行重新綁定。并且，這條規(guī)則也表明了不要將一個(gè)基本類型(如 Int)重新綁定到一個(gè)自定義類型(如 class)上。不要做這種傻事。
### 不要操作超出范圍的內(nèi)存
```swift
// Rule #3... wait
do {
 print("3. Don't walk off the end... whoops!")
 
 let count = 3
 let stride = MemoryLayout<Int16>.stride
 let alignment = MemoryLayout<Int16>.alignment
 let byteCount = count * stride
 
 let pointer = UnsafeMutableRawPointer.allocate(bytes: byteCount, alignedTo: alignment)
 let bufferPointer = UnsafeRawBufferPointer(start: pointer, count: byteCount + 1) // OMG +1????
 
 for byte in bufferPointer {
 print(byte) // pawing through memory like an animal
 }
}

import Foundation
 
enum RandomSource {
 
 static let file = fopen("/dev/urandom", "r")!
 static let queue = DispatchQueue(label: "random")
 
 static func get(count: Int) -> [Int8] {
 let capacity = count + 1 // fgets adds null termination
 var data = UnsafeMutablePointer<Int8>.allocate(capacity: capacity)
 defer {
 data.deallocate(capacity: capacity)
 }
 queue.sync {
 fgets(data, Int32(capacity), file)
 }
 return Array(UnsafeMutableBufferPointer(start: data, count: count))
 }
}

extension Integer {
 
 static var randomized: Self {
 let numbers = RandomSource.get(count: MemoryLayout<Self>.size)
 return numbers.withUnsafeBufferPointer { bufferPointer in
 return bufferPointer.baseAddress!.withMemoryRebound(to: Self.self, capacity: 1) {
 return $0.pointee
 }
 }
 }
 
}
 
Int8.randomized
UInt8.randomized
Int16.randomized
UInt16.randomized
Int16.randomized
UInt32.randomized
Int64.randomized
UInt64.randomized