NativeArray<T0>.UnsafeElementAt

参数

返回

T A ref readonly to a value of type T.

描述

Read-only access to NativeArray.ReadOnly elements by index.

This method is dangerous because it returns reference to the memory that can be destroyed (with Dispose, for instance) and if the ref local is accessed that could lead to undefined results including crash.

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!
}