lua-users home
lua-l archive

[Date Prev][Date Next][Thread Prev][Thread Next] [Date Index] [Thread Index]

On Fri, Nov 22, 2013 at 6:38 AM, H. Conrad Cunningham
<> wrote:
> On Tue, Nov 19, 2013 at 10:26 PM, Philipp Janda <> wrote:
> Also thanks.  Weak tables were not in my "working set" of Lua programming
> features and techniques at the time (or yet for that matter).

Here's the gist for weak keys:

    is_cell = setmetatable({}, {__mode="k"}) -- a table with weak keys

    function cons(a,b)
        local cell = {a,b} -- cell == table: 0x12345678
        is_cell[cell] = true
        return cell

    c = cons(1,2)
    is_cell[c] --> true
    for k,v in pairs(is_cell) do print(k,v) end --> table: 0x12345678, true
    c = nil
    for k in pairs(is_cell) do print(k) end --> nothing

The presence of the key in the weak table does not prevent it from
being garbage collected. There's a chapter in PiL that covers it in
more in depth.

-- Pierre-Yves