Iterator:key() and Iterator:value()?

[ravener]

Iterator:key() and Iterator:value()?

[ravener]

Ah but then that'll also require changing next() and prev() too, not sure if worth it.

I was comparing the iterator interface to https://github.com/marcopompili/lua-leveldb#iterator-example

[Laminariy]

How about not changing next() prev() and read() but providing additional functions?
Something like:
read_key() and read_value() - return only key or value.
next_pos() and prev_pos() - move cursor position without returning anything.
next_key() and next_value() - move cursor position and return only key or value.
is_valid() - checks if current cursor position is valid.

upd:
Oh, and also, if you like this idea, don't you mind if I try to do this?

[ravener]

I think that will make it a bit confusing and add too much noise onto the list of functions.

Another option is to make next(), prev() etc all lower level and expose a __pairs in the iterator as well. Perhaps also take options from db:iterator so it's easy to do things like:

for k, v in pairs(db:iterator({
  start = "key1",
  stop = "key99"
})) do
  print(k, v)
end

Then we can give more lower level flexibility from the methods but users can still use the __pairs for clean lua code.

[Laminariy]

Yeah, that sounds much better.

But there is problem in that particular example. What if there is no "key99" in the database, but there is a key following next to it? How can we understand that we need to stop iteration and return nil? Check all received keys by lexicographic order?

Oh, sure, we can just use seek() to get that next key and iterate all keys before it!

So then maybe just keep iterator low-level for flexibility and make slice() function, so we can do something like this:

for k, v in db:slice(start, stop) do
    -- do something here
end

Where start and stop are optional arguments.
Upd: but I forgot about readoptions... Should we provide them here?

Do we need db.__pairs then?

Upd2: Oh, and crazy idea. Maybe we make db.__call method in addition to db.__pairs, so we can iterate all db by pairs(db) or iterate only slice by pairs(db(start, stop)):

-- iterate all db
for k, v in pairs(db) do
     -- do something here
end

-- iterate only slice
for k, v in pairs(db(start, stop)) do
    -- do something here
end

Upd3: or even

-- provide readoptions as table into __call metamethod
for k, v in pairs(db{readoptions here}) do
    -- do something here
end

-- same, but without pairs()
for k, v in db{readoptions here} do
    -- do something here
end

[ravener]

I got the idea of start/stop from plyvel a leveldb wrapper for python.

Currently my brain is just not working and I don't know how to approach this. To be honest I jumped on this project without any real leveldb experience beforehand.

I'll give it a thinking when I feel like it. But feel free to keep posting comments.