Generic functions for table manipulation, at a lower level than the standard table library.
The project started as a drop-in replacement for the standard table library, incorporating a selection of extra features that have on occasion been requested on the 'lua-l' list (e.g. multiple insert/remove; negative indices; list integrity maintenance). The authors gradually realized that no two Lua users can be made to agree on just which extra features are desirable, and moved to a model of C core functions with a Lua top layer.
The main reasons why the standard table library is fast, are:
- table accessess are done by
lua_rawgetiandlua_rawseti, which directly call a C function with the indices already available as C integers; - temporary values are kept on the stack;
- loops are coded directly in C.
Accordingly, the xtable core C routines perform only tasks that exploit
these techniques. They do only minimal parameter checking and do not
supply default table limits (neither 1 nor #tbl). The intention is
that users can easily implement their own add-ons directly in Lua.
The library contains two sublibraries: xtable.block and xtable.tuple.
xtable.block is designed to be a suitable metatable for a table
that will be used mainly as an array. Every function has the same
first three arguments tbl,a,b and operates on the elements from
tbl[a] to tbl[b], where decreasing keys are taken when a>b.
The functions get, set, copy and trisect are provided in
the C core; concat, insert, remove and sort, which in various
ways offer more than their namesakes from the standard library, are
provided in the Lua top layer.
xtable.tuple is a suite of routines that take ... arguments. The
functions keep, map and collect are provided in the C core;
cache and iter are provided in the Lua top layer. The aim is to
provide not full tuple support, but merely some essential services for
routines that are based on the block routines.
The library is released under the same license as Lua.