Re: Proxy tables
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- Subject: Re: Proxy tables
- From: "Wim Couwenberg" <w.couwenberg@...>
- Date: 2003年7月10日 22:09:19 +0200
> Note that the problems iterating proxy tables are also an issue for
> the lazy-copy approach to copying tables.
The question here is if a lazy-copy table iteration should copy all iterated
values. If so, then that's a bit tricky. If not then the iterator cpairs
defined below could be used. (Of course, being used to lua 4 I forgot all
the necessary explicit == nil and ~= nil tests first... :-) )
do
local copies = {}
setmetatable(copies, {__mode = "k"})
local meta = {
__index = function(table, index)
local t = copies[table]
local v = t[index]
table[index] = v
return v
end,
}
function copy(table)
local c = setmetatable({}, meta)
copies[c] = table
return c
end
function cnext(table, index)
local v
if index == nil or rawget(table, index) ~= nil then
index, v = next(table, index)
if index ~= nil then return index, v end
end
local t = copies[table]
repeat
index, v = next(t, index)
until index == nil or rawget(table, index) == nil
return index, v
end
function cpairs(table)
return cnext, table
end
end
local x = {aap=1, noot=2, mies=3, zus=5}
local y = copy(x)
print(y.noot, y.zus)
for k, v in cpairs(y) do print(k, v) end
--
Wim