获得Memory< byte>可变结构的正确方法/Span< byte&gt ;? [英] Proper way to get a mutable struct for Memory<byte> / Span<byte>?

问题描述

对于网络协议的实现，我想利用新的 Memory 和 Span 类来实现缓冲区的零复制，同时通过结构.

For a network protocol implementation I want to make use of the new Memory and Span classes to achieve zero-copy of the buffer while accessing the data through a struct.

我有以下人为的例子:

[StructLayout(LayoutKind.Sequential, Pack = 1)]
public struct Data
{
    public int IntValue;
    public short ShortValue;
    public byte ByteValue;
}

static void Prepare()
{
    var buffer = new byte[1024];
    var dSpan = MemoryMarshal.Cast<byte, Data>(buffer);
    ref var d = ref dSpan[0];

    d.ByteValue = 1;
    d.ShortValue = (2 << 8) + 3;
    d.IntValue = (4 << 24) + (5 << 16) + (6 << 8) + 7;
}

结果是 buffer 填充了 7、6、5、4、3、2、1 ，这是所需要的，但是我很难想象 MemoryMarshal.Cast 是执行此操作的唯一方法(禁止任何需要 unsafe 关键字的内容).我尝试了其他方法，但无法弄清楚如何将它们与 ref struct (不能用作泛型类型参数)一起使用，或者如何获取位于实际的缓冲区，而不是副本(副本上的任何突变都不会反映在缓冲区上).

The result is that buffer is filled with 7, 6, 5, 4, 3, 2, 1, which is as desired, but I can hardly imagine that MemoryMarshal.Cast is the only way (bar anything requiring the unsafe keyword) to do this. I tried some other methods, but I can't figure out how to use them with either a ref struct (which can't be used as generic type argument) or how to get a struct that's in the actual buffer and not a copy (on which any mutations made are not reflected in the buffer).

有没有更简单的方法从缓冲区中获取此可变结构?

Is there a some easier way to get this mutable struct from the buffer?

推荐答案

Oof.看起来 MemoryMarshal.Cast 是以前的 NonPortableCast 扩展方法(来自:

Oof. It looks like MemoryMarshal.Cast is what used to be the NonPortableCast extension method (from: this commit), in which case - yes, that's the appropriate way to thunk between layouts of spans, most commonly (but not exclusively) like in this case - between byte and some struct.

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