MemoryLayout

MemoryLayout

MemoryLayout //范型
MemoryLayout.size
MemoryLayout.stride
MemoryLayout.alignment

可选项

var age: Int?

强制解包

var num: Int = age!

空合并运算符

let a: Int? =1
let b: Int? =2
let c = a??b

guard 语句

当guard语句的条件为false时，会执行大括号里面的代码
当guard语句的条件为true时，跳过guard语句
guard语句特别适合“提前退出”

隐式解包

var num: Int! = 10
var tmp = num