Swift知识一览（三）

enum Direction {
    case east, south, west, north
}
// 打印该枚举类型所占内存
print(MemoryLayout.size(ofValue: Direction.east)) // 1，解释：1个字节可以存储该枚举类型

// 上述枚举类型，在实际的内存存储中，从east开始存储0，1，2，3

enum CustomNumber {
    case one(Int, Int, Int)
    case two(Int, Int)
    case three(Int)
    case four(Bool)
    case other
}

// 类似上面这种枚举，内存是：
size: 3 * 8 + 1 = 25 // 因为最大关联类型的参数最多有3个，足够存储其他关联类型。1是用来表示存储第几个case
// 查看内存分布的时候，可以看到1字节中存储的是从对应于枚举成员排序的0、1、2、3、4这几个值
alignment: 8
stride: 32

// 只有1个关联类型参数的情况
enum CustomEnum {
    case one(Int)
}
// size、stride、aligment应该都是8（64位平台）。无须存储识别case枚举成员的那1个字节。

/// Invokes the given closure with a pointer to the given argument.
///
/// The `withUnsafePointer(to:_:)` function is useful for calling Objective-C
/// APIs that take in parameters by const pointer.
///
/// The pointer argument to `body` is valid only during the execution of
/// `withUnsafePointer(to:_:)`. Do not store or return the pointer for later
/// use.
///
/// - Parameters:
///   - value: An instance to temporarily use via pointer. Note that the `inout`
///     exclusivity rules mean that, like any other `inout` argument, `value`
///     cannot be directly accessed by other code for the duration of `body`.
///     Access must only occur through the pointer argument to `body` until
///     `body` returns.
///   - body: A closure that takes a pointer to `value` as its sole argument. If
///     the closure has a return value, that value is also used as the return
///     value of the `withUnsafePointer(to:_:)` function. The pointer argument
///     is valid only for the duration of the function's execution.
///     It is undefined behavior to try to mutate through the pointer argument
///     by converting it to `UnsafeMutablePointer` or any other mutable pointer
///     type. If you need to mutate the argument through the pointer, use
///     `withUnsafeMutablePointer(to:_:)` instead.
/// - Returns: The return value, if any, of the `body` closure.
@inlinable public func withUnsafePointer<T, Result>(to value: inout T, _ body: (UnsafePointer<T>) throws -> Result) rethrows -> Result

var dir = Direction.east

let result = withUnsafePointer(to: &dir) { address in
    return address
}
print("--0--dir内存地址--\(result)")