[Lua] 簡易模擬 C# Delegate Type 行為

因為工作需求，準備開始學習 C#，這兩天研究一些公開的 Unity 原始碼發現 C# 有個 Delegate Type 很有意思，它可以利用 + 與 - 將需要搭配執行的 function 指派到委任者然後一起執行。如：

//C#, d1 and d2 are functions
allMethodsDelegate += d1;
allMethodsDelegate += d2;
allMethodsDelegate(); // d1(), d2()
allMethodsDelegate -= d2;
allMethodsDelegate(); // d1()

參考資料：使用委派 (C# 程式設計手冊)

Edit: 03, 08, 2015, 感謝 fb@shanyungyang 的提醒可以使用 Lua 的 metamethod 實作，為了達到屬性能往下傳，本來是打算採用 * / 但是又怕太混亂，最後就是由另外一個 meta2 來達到效果囉! ^^

FuncDelegate2.lua

	-------------------------------------
	-- function delegate part 2
	-- Author: Erin Lin
	-- www.erinylin.com
	-- 簡易模擬 C# delegate
	-- licensed under the MIT license.
	-- 2015, 03
	-- 參考：https://gist.github.com/anonymous/3f0e5b046bfdcfa9864a
	-------------------------------------
	local next = next
	local unpack = unpack
	local t = {
	remove = table.remove,
	insert = table.insert,
	indexOf = function(list, value)
	local n = 0
	for k, v in next, list do
	if v==value then return k end
	end
	return -1
	end
	}
	local meta = {
	__add = function(x, y)
	if type(y) == "function" then
	t.insert(x, y)
	return x
	elseif type(y) == "table" then
	for i=1,#y do
	if type(y[i]) == "function" then t.insert( x, y[i] ) end
	end
	return x
	end
	end,
	__sub = function(x, y)
	if type(y) == "function" then
	local index = t.indexOf( x, y )
	if index > -1 then t.remove( x, index ) end
	return x
	elseif type(y) == "table" then
	for i=#y,1,-1 do
	local index = t.indexOf( x, y[i] )
	if index > -1 then t.remove( x, index ) end
	end
	return x
	end
	end,
	__call = function(d, ...)
	for i,v in next, d do
	v(...)
	end
	end
	}
	local meta2 = {
	__add = meta.__add,
	__sub = meta.__sub,
	__call = function( d, ... )
	local result = arg or {}
	for i,v in next, d do
	result = { v( unpack(result) ) }
	end
	return unpack(result)
	end
	}
	local function newDelegate( bool )
	local d = {}
	--bool==false, use same arguments for every function
	--bool==true, will pass retrun result to next function
	setmetatable(d, bool and meta2 or meta)
	return d
	end
	-------------------------------------
	--
	-------------------------------------
	local function step1( n )
	print("Step1", n, n + 10 )
	return n + 10
	end
	local function step2( n )
	print("Step2", n, n + 20 )
	return n + 20
	end
	local function step3( n )
	print("Step3", n, n + 30 )
	return n + 30
	end
	local d = newDelegate()
	local d2 = newDelegate( true )
	d = d + { step3, step2 }
	d2 = d2 + { step1, step2, step3 }
	print("d(0):")
	d( 0 )
	d = d - step2
	print("d = d - step2 ; d(0)")
	d( 0 )
	print("d2( 100 ):")
	d2( 100 )
	print("-----------------")
	d2 = d2 - step2
	print("d2 = d2 - step2 ; d2(100)")
	d2( 100 )

view raw FuncDelegate2.lua hosted with ❤ by GitHub

這樣拿來組合執行函式實在很方便，所以為了可以在 CoronaSDK 內使用，利用 Lua table 簡單實作類似行為。（當然是沒有辦法寫 + and -，如果不像的話，就是我只實作自己想要的功能啊...XD）
FuncDelegate.lua

	-------------------------------------
	-- function delegate
	-- Author: Erin Lin
	-- www.erinylin.com
	-- 簡易模擬 C# delegate
	-- licensed under the MIT license.
	-- 2015, 02
	-------------------------------------
	--[[
	Usage1:
	local function step1()
	print("Step1")
	end
	local function step2()
	print("Step2")
	end
	local function step3()
	print("Step3")
	end
	local delegate = require("FuncDelegate").new()
	delegate:insert( step1 ):insert( step2 ):insert( step3 )
	-- Output:
	-- Step1
	-- Step2
	-- Step3
	Usage 2:
	local function step1( n )
	print("Step1", n )
	return n + 10
	end
	local function step2( n )
	print("Step2", n )
	return n + 20
	end
	local function step3( n )
	print("Step3", n )
	return n + 30
	end
	local delegate = require("FuncDelegate").new()
	delegate:insert( step1 ):insert( step2 ):insert( step3 )
	print("delegate:run( 0 ) =", delegate:run( 0 ) )
	print("delegate:runWithSameArgs( 0 ) =", delegate:runWithSameArgs( 0 ) )
	-- Output:
	-- Step1 0
	-- Step2 10
	-- Step3 30
	-- delegate:run( 0 ) = 60
	-- Step1 0
	-- Step2 0
	-- Step3 0
	-- delegate:runWithSameArgs( 0 ) = 10
	--]]
	local M = {
	_pool = {}
	}
	local M_mt = {__index=M}
	local unpack = unpack
	local t = {
	remove = table.remove,
	insert = table.insert,
	indexOf = function(list, value)
	local n = 0
	for k, v in next, list do
	if v==value then return k end
	end
	return -1
	end
	}
	function M:insert( element )
	assert( type(element)=="function", "argument must be a type of function")
	local index = t.indexOf( self._pool, element )
	if index<0 then
	t.insert( self._pool, element )
	end
	return self
	end
	function M:remove( element )
	local index = t.indexOf( self._pool, element )
	if index > -1 then
	t.remove( self._pool, index )
	end
	return self
	end
	-- will pass retrun result to next function
	-- 會將前一個函式的回傳值傳到下一個函式，但是如果都是無回傳，用 run or runWithSame 都無所謂
	function M:run( ... )
	local result = arg or {}
	for i=1,#self._pool do
	result = { self._pool[i](unpack( result )) }
	end
	return unpack( result )
	end
	-- use same arguments for every function
	-- 全部函式都用一開始的傳入值
	function M:runWithSameArgs( ... )
	local params = arg or {}
	local result = {}
	for i=1, #self._pool do
	result = { self._pool[i](unpack( params )) }
	end
	-- only return last function's result
	return unpack(result)
	end
	function M:clear()
	for i=#self._pool,1,-1 do
	self._pool[i] = nil
	end
	end
	function M.new()
	local obj = {}
	setmetatable( obj, M_mt )
	obj._pool = {}
	return obj
	end
	return M

view raw FuncDelegate.lua hosted with ❤ by GitHub