Re: Tracking number of pairs in a dictionary

[Doug Currie <doug.currie@...>]

On Oct 1, 2009, at 1:01 PM, Duncan Cross wrote:

> On Thu, Oct 1, 2009 at 5:09 PM, Jorge <xxopxe@gmail.com> wrote:
> > On Wed, 2009-09-30 at 23:34 +0200, Michal Kolodziejczyk wrote:
> > > Or you could keep a counter within the table (so you will not  
> > > iterate
> > > the table at all).


Or you can use closures

function make_LimitedTable (limit)
    local function make_LimitedTable_MT ()
        local n = 0
        local MT={
            add=function(self, key, value)
              if not rawget(self, key) then
                if n >= limit then
                  self:removeOne()
                end
                n = n + 1
              end
              rawset(self, key, value)
            end,
            removeOne=function(self)
              self[next(self)]=nil
                n = n - 1
                print('Removed entry')
            end,
            del=function(self, key)
              if rawget(self, key) and n > 0 then
                n = n - 1
              end
              rawset(self, key, nil)
            end
        }
        MT.__index=MT
        return MT
    end
    return setmetatable({},make_LimitedTable_MT())
end

> t = make_LimitedTable(2)
> t:add('a',{})
> t:add('b',{})
> t:add('c',{})
Removed entry
> for k,v in pairs(t) do print(k,v) end
c	table: 0x10b370
b	table: 0x101b90


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