C function to return tuple

CREATE TYPE d_type AS

(

);

My problem is that I don't know how to construct the d_type tuple in the c function. I read the documentation but it only explains how i could do that for a more simple type like p_type.

The difficulty is that d_type has attributes of p_type.

Thank you in advance.

Datum d_swap(PG_FUNCTION_ARGS) {

    HeapTupleHeader t = PG_GETARG_HEAPTUPLEHEADER(0);

    HeapTupleHeader i;

    HeapTupleHeader e;

    bool isnull;

    TupleDesc tupdesc;

    Datum values[3];

    HeapTuple tuple;

    int tuplen;

    bool *nulls;

    i = DatumGetHeapTupleHeader(GetAttributeByName(t, "i", &isnull));

    e = DatumGetHeapTupleHeader(GetAttributeByName(t, "e", &isnull));

    if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE) {

        ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED), errmsg("function returning record called in context that cannot accept type record")));

    }

    BlessTupleDesc(tupdesc);

    values[0] = e;

    values[1] = i;

    values[2] = GetAttributeByName(t, "id", &isnull);

    tuplen = tupdesc->natts;

    nulls = palloc(tuplen * sizeof (bool));

    tuple = heap_form_tuple(tupdesc, values, nulls);

    pfree(nulls);

    PG_RETURN_DATUM(HeapTupleGetDatum(tuple));

}