Previously, class SQL::Key
depends on def class SQL::IndexDef (because inline def index())
depends on def class SQL::KeyPartDef (inline def key_definition())
depends on def class SQL::ColumnDef (because base class)
depends on def class SQL::Relation (because base class)
depends on def class SQL::Key (because inline def hash()).
This hasn't caused any problems so far because Meta.h happened to be
always included after Key.h (in part due to alphabetical ordering).
However, a compilation that for example only contains
#include <Userland/Libraries/LibSQL/Key.h>
would fail to compile.
This patch resolves this issue by pushing the inline definition of
SQL::Relation::hash() into a different file. Yes, this might reduce
performance marginally, but this gets it to compile again.
The implemtation of the Value class was based on lambda member variables
implementing type-dependent behaviour. This was done to ensure that
Values can be used as stack-only objects; the simplest alternative,
virtual methods, forces them onto the heap. The problem with the the
lambda approach is that it bloats the Values (which are supposed to be
lightweight objects) quite considerably, because every object contains
more than a dozen function pointers.
The solution to address both problems (we want Values to be able to live
on the stack and be as lightweight as possible) chosen here is to
encapsulate type-dependent behaviour and state in an implementation
class, and let the Value be an AK::Variant of those implementation
classes. All methods of Value are now basically straight delegates to
the implementation object using the Variant::visit method.
One issue complicating matters is the addition of two aggregate types,
Tuple and Array, which each contain a Vector of Values. At this point
Tuples and Arrays (and potential future aggregate types) can't contain
these aggregate types. This is limiting and needs to be addressed.
Another area that needs attention is the nomenclature of things; it's
a bit of a tangle of 'ValueBlahBlah' and 'ImplBlahBlah'. It makes sense
right now I think but admit we probably can do better.
Other things included here:
- Added the Boolean and Null types (and Tuple and Array, see above).
- to_string now always succeeds and returns a String instead of an
Optional. This had some impact on other sources.
- Added a lot of tests.
- Started moving the serialization mechanism more towards where I want
it to be, i.e. a 'DataSerializer' object which just takes
serialization and deserialization requests and knows for example how
to store long strings out-of-line.
One last remark: There is obviously a naming clash between the Tuple
class and the Tuple Value type. This is intentional; I plan to make the
Tuple class a subclass of Value (and hence Key and Row as well).
The Order enum is used in the Meta component of LibSQL. Using this enum
meant having to include the monster AST/AST.h include file. Furthermore,
they are sort of basic and therefore can live in the general SQL
namespace. Moved to LibSQL/Type.h.
Also introduced a new class, SQLResult, which is needed in future
patches.
Unfortunately this patch is quite large.
The main functionality included are a BTree index implementation and
the Heap class which manages persistent storage.
Also included are a Key subclass of the Tuple class, which is a
specialization for index key tuples. This "dragged in" the Meta layer,
which has classes defining SQL objects like tables and indexes.
