Do we want to have weakref support?
Here's another thing to consider re: completeness of language implementation: do we want to support weak referenced (weakref module)?
On one hand, it's niche feature used rarely enough. On the other hand, it's something which would pretty much help low-memory usage: ability to cache some object in memory, but safely and transparently free it if there's memory pressure.
But efficient implementation of weakrefs is expensive - each object need to grow to contain pointer to its associated weakref. Taking into account that weakrefs are rare, less runtime-efficient, but much more memory-efficient impl of having a separate mapping from obj to its weakref can be used.
Thoughts/comments are welcome.
Towards possibility of precise garbage collector
It seems that many approaches of further evolution of GC in uPy depend on being able to do precise GC, i.e. tell which fields with an object are pointers are which are not. To achieve this, each allocated memory block has to be explicitly typed (and from type, internal layout can be inferred). Way to achieve this while staying compatible with conservative GC and without updating code largely is to have to set of memory allocation routines: one set is to deal with uPy objects (which already have type header is structure member) and another set to deal with "raw" memory allocations (which will need type header added implicitly for precise GC, and nothing added for conservative GC).
We currently have ~dozen functions to do memalloc. The above means doubling them. Other approach would be to reserve all current functions to uPy objects, add just add 2 funcs for "raw" memory: m_malloc() (will use implicit "all pointers inside" type) and m_malloc_typed() which takes explicit type for allocation.
Other thoughts?