Correct way to read list of mapped values in C#

[dend]

I have a list (BT_LIST) of mapped values (BT_MAP) that seems to contain string values (BT_STRING). I am reading the container data as such (including BT_MAP):

private void ReadContainer(CompactBinaryReader<Bond.IO.Unsafe.InputBuffer> reader)
{
    reader.ReadContainerBegin(out int containerCounter, out BondDataType containerDataType);

    for (int i = 0; i < containerCounter; i++)
    {
        this.DecideOnDataType(reader, containerDataType);
    }

    reader.ReadContainerEnd();
}

It seems, however, that while the function above works for lists and sets, it doesn't work for BT_MAP because I am not fully reading the header data (key type, value type, count). Is there an appropriate routine for this @chwarr?

[dend]

I updated the code a bit - I can read the value data type as well, but still unable to read actual values:

private void ReadContainer(CompactBinaryReader<Bond.IO.Unsafe.InputBuffer> reader, bool isMap = false)
{
    string marker = "Mapped value type: ";
    int containerCounter;
    BondDataType containerDataType = BondDataType.BT_UNAVAILABLE;
    BondDataType valueDataType = BondDataType.BT_UNAVAILABLE;

    if (!isMap)
    {
        reader.ReadContainerBegin(out containerCounter, out containerDataType);
    }
    else
    {
        reader.ReadContainerBegin(out containerCounter, out containerDataType, out valueDataType);
    }

    for (int i = 0; i < containerCounter; i++)
    {
        this.DecideOnDataType(reader, containerDataType);
    }

    reader.ReadContainerEnd();
}

How do I read the full mapped value here?

[chwarr]

Maps are serialized in Compact Binary as contiguous key/value pairs. Your DecideOnDataType doesn't take a valueDataType parameter, so my guess is that it doesn't know how to read the value in each map entry's key/value pair.

The .expressions files under cs/test/expressions show the Linq expressions that each transform generates for the schema in the same directory. Those could be useful to consult to figure out how Bond deserializes a given construct. For example, take a look at the code generated to deserialize 60: map<int32, double> _map. The core loop reads an int32 then a double count times where count is the size that ReadContainerBegin reported.

.Block(
    System.Int32 $Example_result._map_key,
    System.Double $Example_result._map_value) {
    .Default(System.Void);
    .Loop  {
        .If ($count-- > 0) {
            .Block() {
                $Example_result._map_key = .Call $reader.ReadInt32();
                .Default(System.Void);
                $Example_result._map_value = .Call $reader.ReadDouble();
                ($Example_result._map).Item[$Example_result._map_key] = $Example_result._map_value
            }
        } .Else {
            .Break end { }
        }
    }
    .LabelTarget end:

There's a lot more code there, but it's also handling numeric promotions for both the key and the value as well as skipping unknown fields.

[dend]

Aha - I think I see that the right approach here is that once I read the map key, I also need to read the value sequentially. Here is my implementation for it: https://github.com/OpenSpartan/bond-reader/blob/e5a6b454721e81aa3766a8e0eca55aa0e6b73795/src/BondReader/BondProcessor.cs#L101-L109

It seems, at least on the surface, to work - because the value is a struct, it goes into reading the container again and seems to yield the right values back.

Thank you again for helping look into this @chwarr!