如何在Swift中重新解释？ [英] How to reinterpret_cast in Swift?

问题描述

我们的项目依赖于声明通用 struct

Our project depends on a C library that declares a general struct

typedef struct
{
  SomeType a_field;
  char payload[248];
} GeneralStruct

和更具体的一个：

typedef struct
{
  SomeType a_field;
  OtherType other_field;
  AnotherType another_file;
  YetAnotherType yet_another_field;
} SpecificStruct

我们有一些在C ++中使用它的示例，在某些情况下需要将通用对象转换为特定对象，例如：

We have some examples of its usage in C++ and in some cases it's needed to cast the general one to the specific one like:

GeneralStruct generalStruct = // ...
SpecificStruct specificStruct = reinterpret_cast<SpecificStruct&>(generalStruct)

是否是 reinterpret_cast 在Swift中可用吗？我想我可以手动读取 payload 中的字节，但是我正在寻找一种惯用的方式

Is it something like reinterpret_cast available in Swift? I guess I could read the bytes from payload manually, but I'm looking for an idiomatic way

推荐答案

withMemoryRebound（to：容量：_：） 可以使用

...当您将指向内存的指针绑定到一个

... when you have a pointer to memory bound to one type and you need to access that memory as instances of another type.

示例：取通用结构的地址，然后重新绑定并取消引用指针：

Example: Take the address of the general struct, then rebind and dereference the pointer:

let general = GeneralStruct()

let specific = withUnsafePointer(to: general) {
    $0.withMemoryRebound(to: SpecificStruct.self, capacity: 1) {
        $0.pointee
    }
}

如果两种类型具有相同的大小和兼容的内存布局，则还可以使用 unsafeBitCast（_：to：） ：

If both types have the same size and a compatible memory layout then you can also use unsafeBitCast(_:to:):

仅当无法通过其他方式进行转换时，才使用此功能将作为x传递的实例转换为与布局兼容的类型。

Use this function only to convert the instance passed as x to a layout-compatible type when conversion through other means is not possible.

警告：调用此函数将破坏Swift类型系统的保证。

Warning: Calling this function breaks the guarantees of the Swift type system; use with extreme care.

示例：

let specific = unsafeBitCast(general, to: SpecificStruct.self)

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