Enums in Lua (library), Lua

Enums in Lua (library)

--
-- Go to the bottom for a sample
--

do
    -- nilString
    local funcs = {}
    local envMt = {
        __index = function(self, key)
            local fo = funcs[key]
            if fo then
                fo.before()
                return function(...)
                    local returning = fo.func(...)
                    fo.after(...)
                    
                    return returning
                end
            end
            
            return nil
        end,
    }
    setmetatable(_ENV, envMt)
    local nilStringMt = {
        __index = function(self, key)
            return envMt.__index(self, key) or key
        end,
    }
    local function startNilString()
        setmetatable(_ENV, nilStringMt)
    end
    local function stopNilString()
        setmetatable(_ENV, envMt)
    end
    
    -- enum item
    local enumItem = {}
    enumItem.__index = enumItem
    
    enumItem.__tostring = function(self)
        return ("(EnumItem %s)"):format(self.name)
    end
    
    enumItem.__eq = function(self, comparing)
        return self.value == comparing.value
    end
    
    function newEnumItem(value, from, name)
        return setmetatable({
            value = value,
            name = name,
            
            __from = from,
        }, enumItem)
    end
    
    -- enum class
    local enum = {}
    
    enum.__index = function(self, k)
        return self.__keys[k] or enum[k]
    end
    
    local function newEnum(tbl)
        local instance = {__keys = {}}
        
        for keyCount, key in ipairs(tbl) do
            instance.__keys[key] = newEnumItem(keyCount, instance, key)
        end
        
        return setmetatable(instance, enum)
    end
    
    -- enum func
    local enumFunc = {}
    funcs.Enum = enumFunc
    
    function enumFunc.before()
        startNilString()
    end
    
    function enumFunc.func(tbl)
        return newEnum(tbl)
    end
    
    function enumFunc.after()
        stopNilString()
    end
end

--
-- Sample
--
Errors = Enum {
    StringEmpty, Success
}

function say(str)
    if str == "" then
        return Errors.StringEmpty
    end
    
    print(str)
    return Errors.Success
end

local Success = say("")

if Success == Errors.StringEmpty then
    print("String empty!")
    return
end

print("Success!")


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