Provide macro to declare pre-inited tables

[RicBent]

Hi, thanks for your work! Really appreciate the clean api and efficiency it brings to the (vers)table.

In my use case, I have many tables as global state. As they are static and spread across multiple TUs, all of them previously needed a <module>_init() function that just calls vt_init for all contained tables.

To remove this need, I simply added this macro:

#define VT_INITED {.metadata = (uint16_t*)&vt_empty_placeholder_metadatum}

For better compatibility with pre-C99 and pre-C++20 it could also be defined as:

#define VT_INITED {0, 0x0000000000000000ull, NULL, (uint16_t*)&vt_empty_placeholder_metadatum}
#define VT_INITED_WITH_CTX(ctx) {0, 0x0000000000000000ull, NULL, (uint16_t*)&vt_empty_placeholder_metadatum, ctx}

This allows simply defining global tables like this without the need for any runtime initializer:

static my_table_t s_table = VT_INITED;

One thing I am unsure about with this design: Destructors still need to be called manually. Not avoidable, but this may be missed by users as you can easily forget about that if you do not ever call vt_init manually.

I still think this would be pretty useful addition. What do you think?

Best regards

[JacksonAllan]

Hi Ric! Sorry for the delayed response.

That's a great idea. In fact, CC already provides this exact feature via the cc_initialized macro. I'll incorporate it into the next Verstable release.

One thing I am unsure about with this design: Destructors still need to be called manually.

This shouldn't be a problem, I think. Destructor calls are inserted directly into the code generated via the template instantiation process - you can see how they're handled using #ifdef/#endif sections in _erase, for example, here. In other words, destructors are not called via any function pointer set in _init.

I'm not too sure when the next release is coming. Hopefully soon as there are already a few improvements queued up. I've been pretty distracted with a new SIMD hash table design that - if it come to fruition as a new library - will implement much the same API as Verstable.