Re: tables as keys
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- Subject: Re: tables as keys
- From: Luis Carvalho <carvalho@...>
- Date: 2008年3月11日 11:08:49 -0400
> For instance, I want to do something like:
>
> t = makeASpecialTable()
> t[{a=1, b=2}] = 42
> assert(t[{a=1, b=2}] == 42)
Here are my $.02:
-- special.lua
local pairs, setmetatable = pairs, setmetatable
local assert, type, tostring = assert, type, tostring
local sort = function(t)
-- tostring can be any serializer
table.sort(t, function(x, y) return tostring(x) < tostring(y) end)
end
module(...)
-- sorted-key table iterator
local sk = setmetatable({}, { -- sorted refs
__index = function(t, k)
local s = {}
for kk in pairs(k) do
s[#s + 1] = kk
end
sort(s)
t[k] = s
return s
end,
__mode = "k"
})
local function skpairs (t)
local s, i = sk[t], 0
return function()
i = i + 1
local k = s[i]
local v = t[k]
if v ~= nil then return k, v end
end
end
function new ()
local o = {}
return setmetatable({}, {
__newindex = function(_, k, v)
assert(type(k) == "table")
local i, n, h = 0, #sk[k], o
for kk, kv in skpairs(k) do
i = i + 1
local t = h[kk]
if t == nil then
t = {}
h[kk] = t
end
h = t
t = h[kv]
if t == nil then
t = i == n and v or {}
h[kv] = t
end
h = t
end
end,
__index = function(_, k)
assert(type(k) == "table")
local v = o
for kk, kv in skpairs(k) do
v = v[kk]
if v ~= nil then v = v[kv] end
if v == nil then return nil end
end
return v
end
})
end
$ lua -lspecial
Lua 5.1.2 Copyright (C) 1994-2007 Lua.org, PUC-Rio
> t = special.new()
> t[{a=1, b=2}] = 42
> = t[{a=1, b=2}]
42
Cheers,
Luis.
--
A mathematician is a device for turning coffee into theorems.
-- P. Erdos
--
Luis Carvalho
Applied Math PhD Student
Brown University