nominal.luau

--!strict

type function default_nanoid()
    return nanoid()
end

export type function nominal(input: type)
    local phantom_table = types.newtable()
    phantom_table:setwriteproperty(types.singleton("_phantom_nominal_id"), types.singleton(default_nanoid()()))

    return types.intersectionof(input, phantom_table)
end


-- The nanoid type function was forked from `actboy168`'s lua nanoid implementation.
-- License below:
--[[
    MIT License

    Copyright (c) 2024 actboy168

    Permission is hereby granted, free of charge, to any person obtaining a copy
    of this software and associated documentation files (the "Software"), to deal
    in the Software without restriction, including without limitation the rights
    to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
    copies of the Software, and to permit persons to whom the Software is
    furnished to do so, subject to the following conditions:

    The above copyright notice and this permission notice shall be included in all
    copies or substantial portions of the Software.

    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
    SOFTWARE.
]]

type function countl_zero(x)
    local n = 32
    local y = bit32.rshift(x, 16)
    if y ~= 0 then
        n = n - 16
        x = y
    end
    y = bit32.rshift(x, 8)
    if y ~= 0 then
        n = n - 8
        x = y
    end
    y = bit32.rshift(x, 4)
    if y ~= 0 then
        n = n - 4
        x = y
    end
    y = bit32.rshift(x, 2)
    if y ~= 0 then
        n = n - 2
        x = y
    end
    y = bit32.rshift(x, 1)
    if y ~= 0 then
        n = n - 1
        x = y
    end
    return n - x
end

type function nanoid(alphabet: string?, size: number?)
    local alphabet = alphabet or "_-0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
    local size = size or 21

    local RandomMaxBit = 31
    local RandomMax = bit32.lshift(1, RandomMaxBit) - 1

    local alphabet_table = {}
    for c in string.gmatch(alphabet, ".") do
        alphabet_table[#alphabet_table + 1] = c
    end

    local mask_bit = 32 - countl_zero(#alphabet_table - 1)
    local mask = bit32.lshift(1, mask_bit) - 1
    local id = {}

    if #alphabet_table == mask + 1 then
        local step = RandomMaxBit // mask_bit
        local suffix = (size // step) * step
        if suffix == size then
            return function()
                for cnt = 1, size - step + 1, step do
                    local rnd = math.random(0, RandomMax)
                    for i = 0, step - 1 do
                        local index = 1 + bit32.band(bit32.rshift(rnd, i * mask_bit), mask)
                        id[cnt + i] = alphabet_table[index]
                    end
                end
                return table.concat(id)
            end
        else
            return function()
                for cnt = 1, size - step + 1, step do
                    local rnd = math.random(0, RandomMax)
                    for i = 0, step - 1 do
                        local index = 1 + bit32.band(bit32.rshift(rnd, i * mask_bit), mask)
                        id[cnt + i] = alphabet_table[index]
                    end
                end
                local rnd = math.random(0, RandomMax)
                for cnt = suffix + 1, size do
                    local index = 1 + bit32.band(bit32.rshift(rnd, (cnt - suffix - 1) * mask_bit), mask)
                    id[cnt] = alphabet_table[index]
                end
                return table.concat(id)
            end
        end
    else
        return function(): string
            local cnt = 1
            while true do
                local rnd = math.random(0, RandomMax)
                for i = 0, RandomMaxBit - mask_bit, mask_bit do
                    local index = 1 + bit32.band(bit32.rshift(rnd, i), mask)
                    if index <= #alphabet_table then
                        id[cnt] = alphabet_table[index]
                        cnt = cnt + 1
                        if cnt > size then
                            return table.concat(id)
                        end
                    end
                end
            end
        end
    end
end

return nil

Really hacky faked nominal types in luau by intersecting a type with a table with a uuid.

Example usage:

type Name = nominal<string>

local function verify_name(str: string): Name
    return (str :: any) :: Name
end

local function get_email_for_name(name: Name)
    -- gets email
    return "[email protected]"
end

local email = get_email_for_name("hello")

local email = get_email_for_name(verify_name("hello"))