NativeArray<T0>.UnsafeElementAt

参数

返回值

T 一个 ref readonly，指向类型为 T 的值。

描述

通过索引提供对 ReadOnly 元素的只读访问。

此方法很危险，因为它返回对可以被销毁的内存的引用（例如，使用 Dispose），如果访问 ref local，可能会导致未定义的结果，包括崩溃。

public readonly struct BigStruct
{
    public readonly long a;
    public readonly long b;
    public readonly long c;
    public readonly long d;
}

static void ProcessByte(byte b)
{
    ...
}

static void ProcessBigStructWithoutCopy(in BigStruct bigStruct) // see 'in' modificator
{
    ...
}

static void Example()
{
    const int n = 32;

    var nativeArrayOfBytes = new NativeArray<byte>(n, Allocator.Temp);
    var nativeArrayOfBigStructures = new NativeArray<FixedString4096Bytes>(n, Allocator.Temp);

    // ... fill the arrays with some data ...

    var readOnlyBytes = nativeArrayOfBytes.AsReadOnly();
    for (var i = 0; i < n; ++i)
    {
        ProcessByte(readOnlyBytes[i]);
        //ProcessByte(readOnlyBytes.UnsafeElementAt(i)); is more expensive, since pointer on x64 platforms is 8 times bigger than a byte
    }

    var readOnlyBigStructures = nativeArrayOfBigStructures.AsReadOnly();
    for (var i = 0; i < n; ++i)
    {
        //ProcessBigStructWithoutCopy(readOnlyBigStructures[i]); copy - expensive in this case
        ProcessBigStructWithoutCopy(readOnlyBigStructures.UnsafeElementAt(i));
    }

    // dangerous part
    ref var element = ref readOnlyBigStructures.UnsafeElementAt(4);

    // element is valid here
    ProcessBigStructWithoutCopy(element);

    nativeArrayOfBigStructures.Dispose();

    // access to element here is undefined, can lead to a crash or wrong results
    // ProcessBigStructWithoutCopy(element); <-- do not do this!
}