Proper way to assign to *anyopaque

Help
1

I’m trying to assign to a void * handed to me from sdl. Assigning to the dereferenced pointer is a type mismatch. @memset expects dest to be a slice. Is there an idiomatic way to do this kind of assignment? Can I cast *anyopaque to a slice with a runtime-known size? Thanks in advance

const mappedTransferBuffer = sdl.SDL_MapGPUTransferBuffer(device, vertexTransferBuffer, false);
if(mappedTransferBuffer == null) sdl_err();
//@memset(mappedTransferBuffer.?, vertexData);
mappedTransferBuffer.?.* = vertexData;
2

If you want to cast mappedTransferBuffer you can do it as follows:

const ptr : [*]type_of_element = @ptrCast(@alignCast(mappedTransferBuffer));
const slice = ptr[0..len_of_buffer];
3

Many thanks! new code is compiling:

    const mappedTransferBuffer = sdl.SDL_MapGPUTransferBuffer(device, vertexTransferBuffer, false);
    if(mappedTransferBuffer == null) sdl_err();
    const mappedPtr: [*]@TypeOf(vertexData[0]) = @ptrCast(@alignCast(mappedTransferBuffer));
    const mappedSlice = mappedPtr[0..vertexData.len];
    mappedSlice.* = vertexData;
4

Is there a reason you don’t return for the null situation?

5

sdl_err() panics so there’s no need

6

I would still do an explicit return or unreachable there.