Cannot determine specific type of datatype

[enkoder]

I need to be able to read a dataset into memory, but cannot create a struct for each dataset because of some difficult requirements of my project.

I would like to be able to read a compound dataset with an unknown format into memory by using a slice := []interface{} but in order for me to set the underlying memory for each element I need to get the specific type for each member of the compound dataset. So I need to know whether the datatype is a uint8, float32, int64, string, etc.

Currently, from what I know so far, I can only get the high level types using the Dataset.Class() function. I can check the Dataset.Size() value to know the size of each type, but I dont have any knowledge if the value is unsigned or signed.

Here is what I have cooking up so far, I think I am close:

var i uint
for i = 0; i < numDsets; i++ {
    dsetName, err := f.CommonFG.ObjectNameByIndex(i)
    table, err := f.OpenTable(dsetName)
    numRows, err := table.NumPackets()
    dset, err := f.OpenDataset(dsetName)
    dtype, err := dset.Datatype()
    fmt.Printf("\n%s: %d\n", dsetName, numRows)
    if dtype.Class() == h5.T_COMPOUND {
        comp := h5.CompoundType{
            Datatype: *dtype,
        }
        numMembers := comp.NMembers()
        container := make([]interface{}, numMembers)
        for i := 0; i < numMembers; i++ {
            memberClass := comp.MemberClass(i)
            switch memberClass {
            // Right here I would switch on types to be able to set the interface value to the correct type
            // But I dont know how to determine if its a uint8 for example 
            case h5.T_INTEGER:
                container[i] = new(int)
            default:
                container[i] = new(int)
            }
        }
        err = table.ReadPackets(0, 1, &c)
    }
}

For each high level class I can also switch on the size value and set the interface that way, but it feels clunky. Is there a better way for me to be doing this? Thanks in advance.

[sbinet]

untested, but one way would be to retrieve the matching go type from the Datatype:

dtype, err := dset.Datatype()
gotype := dtype.GoType()
switch gotype.Kind() {
    case reflect.Uint8:
        container[i] = new(uint8)
    case reflect.Int64:
        container[i] = new(int64)
    case reflect.Struct:
    // etc...
}
// or directly:
container[i] = reflect.New(gotype).Interface()

https://godoc.org/github.com/sbinet/go-hdf5#Datatype.GoType

[enkoder]

Thanks for the response sbinet. After I posted the initial issue I tried that exact method of using reflect.New() but I hit the following issue.

panic: runtime error: cgo argument has Go pointer to Go pointer

goroutine 1 [running]:
panic(0x70f0a0, 0xc82000a730)
    /usr/lib/go/src/runtime/panic.go:481 +0x3e6
github.com/sbinet/go-hdf5._cgoCheckPointer0(0x6703c0, 0xc8200e6000, 0x0, 0x0, 0x0, 0x197)
    ??:0 +0x4d
github.com/sbinet/go-hdf5.(*Table).ReadPackets(0xc8200d8038, 0x0, 0x1, 0x6598e0, 0xc8200de080, 0x0, 0x0)

I dont think that I will be able to read packets into a slice of interfaces because the underlying implementation of interfaces.I haven't found a way to read variable packets yet. I am unfamiliar with the hdf5 C API, but I am about to dive in to get a better understanding. If you have any thoughts on the matter, I would love to hear them thanks.