Need evaluation on switch statement utility

[Zeros]

Hi, I need someone to evaluate which piece of code should used on rendering call. To be honest, I'm thinking of scrapping the FIRST VERSION because it's recreating table and closure. Worst case is recreating the closure on each call. I might be wrong about this hence I need someone to point out what I'm missing. I would appreciate it if there's better idea to improve the first version because variation one coding style is much more familiar.

 

local validate = function(t)
  if (not t) then
    error("Switch: Argument is nil", 2)
  elseif (type(t) ~= "table") then
    error("Switch: Argument is not a table", 2)
  end
end

-- First Version
local switch = function(val)
  return function(t)
    validate(t)
    if t[val] then
      return t[val]()
    else
      return t["default"]()
    end
  end
end

-- Variation 1
local function render(...)
  local i = 10
  switch(i) {
    [1] = function()
      print("One")
    end,
    [10] = function()
      print("Ten")
    end,
    default = function()
      print("Unknown value!")
    end,
  }
end

-- Variation 2
local tSwitch = {}
local function render(...)
  local i = 10
  tSwitch.Value = tSwitch.Value or {
    [1] = function()
      print("One")
    end,
    [10] = function()
      print("Ten")
    end,
    default = function()
      print("Unknown value!")
    end,
  }
  switch(i)(tSwitch.Value)
end

-- Second Version
local switch = function(val, t)
  validate(t)
  if t[val] then
    return t[val]()
  else
    return t["default"]()
  end
end

local tSwitch = {}
local function render(...)
  local i = 10
  tSwitch.Value = tSwitch.Value or {
    [1] = function()
      print("One")
    end,
    [10] = function()
      print("Ten")
    end,
    default = function()
      print("Unknown value!")
    end,
  }
  switch(i, tSwitch.Value) 
end

 

Edited August 25, 2022 by Zeros

[Zeros]

I encountered a critical issue when using the second version. Since the switch function is defined once without getting values from the table function arguments, it will use the very first upvalue, meaning that the function will not receive any new data. Therefore, I've added variable arguments parameter to the switch function.

 

local validate = function(t)
	if (not t) then
		error("Switch: Argument is nil", 2)
	elseif (type(t) ~= "table") then
		error("Switch: Argument is not a table", 2)
	end
end

local switch = function(val, t, ...)
	validate(t)
	local args = {...}
	if t[val] then
		if (#args > 0) then
			return t[val](unpack(args))
		else
			return t[val]()
		end
	else
		return t["default"]()
	end
end

local tSwitch = {}

-- Example One - Without Arguments
do
  tSwitch.Value = tSwitch.Value or {
    [1] = function()
      print("One")
    end,
    [2] = function()
      print("Two")
    end,
    [3] = function()
      print("Three")
    end,
    [4] = function()
      print("Four")
    end,
    [5] = function()
      print("Five")
    end,
    default = function()
      print("Unknown value!")
    end,
  }
  for i=1, 6 do
    switch(i, tSwitch.Value)
  end
end

--Example Two - With Arguments
do
  tSwitch.Var = tSwitch.Var or {
    ["add"] = function(i1, i2)
      print(i1 + i2)
    end,
  }
  switch("add", tSwitch.Var, 5, 10)
end