浅析Swift中枚举的内存布局

对于一般的定义方式:

enum Direction {
      case north, south, east, west
}

对于内存的打印，我使用的github上的工具(工具连接),并且打印对象的分配大小、实际使用大小、内存对齐大小，代码如下:

var dir = Direction.north
print(Mems.ptr(ofVal: &dir))
dir = .south
dir = .east
 dir = .west
 print(MemoryLayout.stride(ofValue: dir))
 print(MemoryLayout.size(ofValue: dir))
 print(MemoryLayout.alignment(ofValue: dir))

打印结果如下:

0x00007ffeec8ef1c0
1
1
1

根据打印结果，分配内存为1个字节、实际内存为1个字节、内存对齐为1个字节

若改变声明方式，声明的时候赋值原始值

enum Direction: Int {
        
    case north = 4, south = 5, east = 6, west = 7
}

内存打印和上次一样，但是我对其进行每次赋值，为了区分从四开始赋值，每次地址打印储存值的打印情况如下:

00 00 00 00 赋值为north
01 00 00 00 赋值为south
02 00 00 00 赋值为east
03 00 00 00 赋值为weast

根据打印结果，枚举地址存储的并不是原始值

若生命值变为：

enum TestEnum {
      case test1(Int, Int, Int, Int)
      case test2(Int, Int, Int)
      case test3(Int)
      case test4(Bool)
      case test5
 }

此时我打印内存输出结果:

0x00007ffeeadad1a0
40
33
8

总大小为40个字节可以推算出是根据最大的test进行分配，4 个 int 32个字节，然后加上1 个字节，但是由于内存对齐需要8个字节，也就对应了总的字节数32 + 8，实际

使用的字节数32 + 1，内存对齐为8

当初始化代码为:

var dir = TestEnum.test1(1, 1, 1, 1)

01 00 00 00 00 00 00 00 
01 00 00 00 00 00 00 00 
01 00 00 00 00 00 00 00 
01 00 00 00 00 00 00 00 
00
00 00 00 00 00 00 00

根据此时的内存打印对应我们之前预想的内存分配

当初始化为:

dir = TestEnum.test2(3, 3, 3)

03 00 00 00 00 00 00 00 
03 00 00 00 00 00 00 00 
03 00 00 00 00 00 00 00 
00 00 00 00 00 00 00 00
01 
00 00 00 00 00 00 00

上面大概就是枚举的内存分配