function fmsg(fmt_str, ...)
    message(fmt_str:format(...))
end

TableFilter ={}
TableFilter.__index = TableFilter
function TableFilter.new(t_name)

    filter = {}
    filter.table_name = t_name
    filter.selected_items = {}
    filter.pattern = {}
    filter.start_index=0
    filter.end_index = 0
    setmetatable(filter, TableFilter)
    return filter
end

function TableFilter:SetFilter(t)
    self.pattern = t
end

function TableFilter:SetRange(s, e)
        self.start_index = s or 0
        self.end_index = e or (getNumberOf(self.table_name)-1)
end

function TableFilter:Left()
    return self.start_index
end

function TableFilter:Right()
    return self.end_index
end

function TableFilter:Update()
    local fields = ""
    local t={}
    for k,v in pairs(self.pattern) do
        fields = fields .. ',' .. tostring(k)
        t[#t+1] = v
    end
    local function fn(...)
        local arg = {...}
        local res=true
        for k,v in ipairs(arg) do
            if t[k] ~= v then
                res = false
                break
            end
        end
        return res
    end
    self.selected_items = SearchItems(self.table_name, self.start_index, self.end_index, fn, fields)
end

function TableFilter:Result()
    local index = 1
    return function()
        if (self.selected_items[index]) then

            local t = getItem(self.table_name, self.selected_items[index])
            index = index+1
            return t
        end
        return nil
    end
end
function TableFilter:GetResultSize()
    return #(self.selected_items)
end
function main()
    filter = TableFilter.new("all_trades")
    filter:SetRange()
    filter:SetFilter {sec_code = 'RIM6', class_code = 'SPBFUT', qty = 1}

    _start = os.clock()
    for i = 1, 100 do
        filter:Update()
    end
    _end = os.clock()

    fmsg("found %d, took %.3f sec" , filter:GetResultSize(), _end-_start)
end