Introduce Bool Type

[IyeOnline]

Previously the library implicitly converted bool columns to Uint8,
loosing type information.

This commit introduces a "strong type" for Bool that is distinct from
bool. This allows complete re-use of ColumnVector without triggering
the std::vector<bool> specialization.

This new type is guarded behind a CMake variable/preprocessor define
CH_MAP_BOOL_TO_UINT8, which is enabled by default in order to keep
compatibility for library users. In the future the default should be
switched first and the variable then removed later.

• Fixes Add Bool type support (distinct from UInt8) #476

[slabko]

@IyeOnline, I think I’m missing something here, but how am I supposed to use it for inserting values? The obvious way of using the actual type doesn’t look right to me:

col_bool->Append(clickhouse::Bool::true_);
col_bool->Append(clickhouse::Bool::false_);

This doesn’t look any better either:

col_bool->Append(static_cast<clickhouse::Bool>(true));
col_bool->Append(static_cast<clickhouse::Bool>(false));

I was wondering whether you considered simply subclassing ColumnVector<uint8_t>?

[IyeOnline]

@slabko You can do col_bool->Append(Bool{true});, potentially with a using ::clickhouse::Bool in scope - which really isnt much better.

I only tested getting values out on my side (because thats what I need it for) and there the clickhouse::Bool -> bool conversion is implicit. I actually intended for this to work without any extra specifications and it clearly does not. :|

I did think about sub-classing a uint8 column originally as a means of having seamless compatibility but discarded that idea as it would still clash with the Type::Code.

Further, I think for correctness you would want the ColumnBool to only privately inherit ColumnVector<uint8_t> as its only an implementation detail. This made it not very appealing, since you then need to introduce virtual inheritance and a bunch of using declarations to get public members form the private base back.

But looking at the Append issue (which I missed/thought would work), I think that is indeed the way to go.

[IyeOnline]

@slabko I went with composition instead of inheritance, as I think it would be preferable to not be able to cast a column with type == Bool to UInt8, but I dont have a strong opinion on this. Private inheritance would have required making every inheritance virtual, which would have required larger changes (e.g. not being able to static_cast in a bunch of places).

[slabko]

@IyeOnline I think composition is even better and provides much more flexibility.
Do you have a chance to look at the MSVC build? It seem to be failing on CI.