Is there a way to represent a range of indexes in a lua table for a dissector?

Question

Trying to build a dissector in lua where in the ProtoField for one of the values, I map it to a table so that when passed some uint it can get said string from the list of outputs. The current issue is that I have some indexes of 1, 2, and 3, but I also need a range of numbers that correspond to one output string, and its too many to hardcode it all in. I thought about just adding some check that will add said index whenever it doesn't exist, but that would result in alot of wasted time and wanted to ensure there wasn't a better way.

Tried mapping it to a function and setting a default value with a metatable.

Answer 1

Generically, a table can contain tables as indices. These tables could each be used to represent a range of indices.

A cursory example (note that overlapping ranges are not stable):

local range_mt = {}
range_mt.__index = range_mt

function range_mt:contains(value)
    return self.lower <= value and value <= self.upper
end

local function range(lower, upper)
    return setmetatable({
        lower = lower,
        upper = upper
    }, range_mt)
end

local map = setmetatable({
    [1] = 'hello',
    [2] = 'world',
    [3] = 'goodbye',
    ranges = {
        [range(10, 20)] = 'foo',
        [range(51, 99)] = 'bar'
    }
}, {
    __index = function (self, value)
        for r, str in pairs(self.ranges) do
            if r:contains(value) then
                return str
            end
        end

        return "DEFAULT"
    end
})

for _, value in ipairs { 9, 6, 1, 2, 16, 4, 15, 66, 51, 3, 94 } do
    print(value, '->', map[value])
end

9   ->  DEFAULT
6   ->  DEFAULT
1   ->  hello
2   ->  world
16  ->  foo
4   ->  DEFAULT
15  ->  foo
66  ->  bar
51  ->  bar
3   ->  goodbye
94  ->  bar