Writer API Alternatives

Previously we're deserializing FColor by writing into its member fields separately, which is a bit cumbersome. In this case DataConfig do support better alternatives.

Since we know that FColor is POD type we can construct one by filling in correct bit pattern. In this case FDcPropertyWriter allow struct property to be coerced from a blob:

• DcSerDeColor.h
• DcSerDeColor.cpp

//  DataConfigExtra/Private/DataConfig/Extra/SerDe/DcSerDeColor.cpp
template<>
FDcResult TemplatedWriteColorDispatch<EDcColorDeserializeMethod::WriteBlob>(const FColor& Color, FDcDeserializeContext& Ctx)
{
    return Ctx.Writer->WriteBlob({
        (uint8*)&Color, // treat `Color` as opaque blob data
        sizeof(FColor)
    });
}

Alternatively we can get FProperty and data pointer in place and setting the value through Unreal's FProperty API:

//  DataConfigExtra/Private/DataConfig/Extra/SerDe/DcSerDeColor.cpp
template<>
FDcResult TemplatedWriteColorDispatch<EDcColorDeserializeMethod::WriteDataEntry>(const FColor& Color, FDcDeserializeContext& Ctx)
{
    FDcPropertyDatum Datum;
    DC_TRY(Ctx.Writer->WriteDataEntry(FStructProperty::StaticClass(), Datum));

    Datum.CastFieldChecked<FStructProperty>()->CopySingleValue(Datum.DataPtr, &Color);
    return DcOk();
}

Note that we already know that Datum.DataPtr points to a allocated FColor instance. Thus we can simply cast it into a FColor* and directly manipulate the pointer.

//  DataConfigExtra/Private/DataConfig/Extra/SerDe/DcSerDeColor.cpp
template<>
FDcResult TemplatedWriteColorDispatch<EDcColorDeserializeMethod::WritePointer>(const FColor& Color, FDcDeserializeContext& Ctx)
{
    FDcPropertyDatum Datum;
    DC_TRY(Ctx.Writer->WriteDataEntry(FStructProperty::StaticClass(), Datum));

    FColor* ColorPtr = (FColor*)Datum.DataPtr;
    *ColorPtr = Color;  // deserialize by assignment

    return DcOk();
}

Note that these techniques also applies on serialization:

//  DataConfigExtra/Private/DataConfig/Extra/SerDe/DcSerDeColor.cpp
FDcResult HandlerColorSerialize(FDcSerializeContext& Ctx)
{
    FDcPropertyDatum Datum;
    DC_TRY(Ctx.Reader->ReadDataEntry(FStructProperty::StaticClass(), Datum));

    FColor* ColorPtr = (FColor*)Datum.DataPtr;
    DC_TRY(Ctx.Writer->WriteString(TEXT("#") + ColorPtr->ToHex()));

    return DcOk();
}