Re: Proxy tables

["Wim Couwenberg" <w.couwenberg@...>]

> 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