I'm completely new to nim and I'm trying to reproduce this pascal type so that I can read a response from a socket into it...

TUDPData=packed record
    DataType:   word;
    SubType:    word;
    Chan:       word;
    Len:        word;
    Data:       packed record
                      case byte of
                      0:(AsChannelStatus01: TChannelStatus01);
                      1:(AsVoltageList: packed array[0..127] of single);
                      2:(AsCurrentList: packed array[0..127] of single);
                      3:(AsAuxValues: packed array[0..47] of single);
                      4:(AsAuxEU: packed array[0..47] of packed array[0..3] of AnsiChar);
                      5:(AsChannelSpec: TChannelSpec);
                      6:(AsSafetySpec: TSafetySpec);
                      7:(AsStartData01: TStartData01);
                      8:(AsVersionInfo: TVersionInfo);
                      9:(AsTestNameAndComments: TTestNameAndComments);
                      10:(AsSMBInfoStatus: TSMBInfoStatus);
                      11:(AsSMBScanListEntry: TSMBScanListEntry);
                      12:(AsSMBGenericWrite: TAsSMBGenericWrite);
                      13:(AsSMBGenericRead: TAsSMBGenericRead);
                      140:(AsSMBGenericReadData: TAsSMBGenericReadData);
                      14:(AsSystemInfo: TSystemInfo);
                      15:(AsCalDates: TCalDates);
                      16:(AsChannelStatus: TAsChannelStatus);
                      17:(AsChannelVARS: TAsChannelVARS);
                      18:(AsStartDirectMode: TAsStartDirectMode);
                      19:(AsSetOutputDirectMode: TAsSetOutputDirectMode);
                      20:(AsSetVAR: TAsSetVAR);
                      252:(AsSingles: packed array[0..127] of single);
                      253:(AsDWords: packed array[0..127] of dword);
                      254:(AsWords: packed array[0..255] of word);
                      255:(AsBytes: packed array[0..511] of byte);

so I know I can just create a union like so:

    TUDPData {.packed.} = object
            , sub_data_type
            , channel
            , len: uint16
            data: Data
    Data {.packed.} = object {.union.}
        version_info: VersionInfo
        system_info: SystemInfo
        name: TestNameAndComments
        channel_status: ChannelStatus
        channel_status_matrix: array[128, LimitedChannelStatus]

but I feel like I'm translating this wrong and I should be using object variants probably. I'm fairly green and just trying to learn so just a push in the right direction or some reading material would be super helpful.

2017-10-09 20:41:04

Nim's object variants are from Pascal, they are what you need. Smth like:

Data = object {.packed.}
            case b: byte
            of 0:  AsChannelStatus01: TChannelStatus01
            of 1: AsVoltageList: array[0..127, single]
            # ...
            else: discard

2017-10-10 10:14:19
object variants are not exactly the same, because you always need the extra tag - byte b here. In pascal you don't need a stored tag (like in the question). I guess the union should result in the same memory layout. 2017-10-10 14:53:57
Right, I need the exact same memory layout as I cant alter the server code, only the client side so I'll stick with the union I guess. Thank you 2017-10-10 14:58:30