[C++] timestamp type for rounding tripping TupleRange <-> Table

[Blair Azzopardi]

Hi

What timestamp type can I use when converting a table to a tuple (& vice
versa)? I seem to have ended up with the c_type but this doesn't round
trip. I'm wondering if I need to implement a ConversionTraits
specialization. Also are there any existing helper functions for converting
between arrow timestamp types and chrono time_points?

The following snippet :

inline Status Main() {
    auto read_options = json::ReadOptions::Defaults();
    auto parse_options = json::ParseOptions::Defaults();
    parse_options.unexpected_field_behavior =
        json::UnexpectedFieldBehavior::InferType;

    std::string json1 =
        R"({"a": 2.0, "b": "foo", "c": "2020-01-01"}
    {"a": -5.5, "b": null, "c": "2020-01-02"}
    )";
    ARROW_ASSIGN_OR_RAISE(auto tab1,
                          ReadToTable(json1, read_options, parse_options));
    cout << tab1->ToString() << endl;

    // what should i use for my timestamp type to ensure round trip?
    vector<tuple<double, string, TimestampType::c_type>> rows(2);

    compute::ExecContext ctx;
    compute::CastOptions cast_options;
    if (!stl::TupleRangeFromTable(*tab1, cast_options, &ctx, &rows).ok()) {
        throw runtime_error("Failed to convert table to tuple range");
    }

    shared_ptr<Table> tab2;
    vector<string> names = {"A", "B", "C"};
    if (!stl::TableFromTupleRange(default_memory_pool(), rows, names, &tab2)
             .ok()) {
        throw runtime_error("Failed to convert tuple vector to table");
    }
    cout << tab2->ToString() << endl;

    return Status::OK();
}

outputs:

a: double
b: string
c: timestamp[s]
----
a:[[2, -5.5]]
b:[["foo", null]]
c:[[2020-01-01 00:00:00, 2020-01-02 00:00:00]]

A: double not null
B: string not null
C: int64 not null
----
A:[[2, -5.5]]
B:[["foo", ""]]
C:[[1577836800, 1577923200]]

Ignoring null vs not-nulls, you can see the column c are integers.

Thanks in advance!