DZone Snippets: Kergoth's Code Snippets

Lua: API deprecation

kergoth (Chris Larson) — Tue, 06 Dec 2005 03:39:23 GMT

What follows is Tem's code to deprecate an API function or table in Lua.

function deprecate(o,name,instead)

	local msg = "%sWarning, deprecated feature "..(name and ("'"..name.."' ") or "").."in use."..(instead and ("  Use '"..instead.."' instead.") or "")

	if(type(o) == "table") then

		return setmetatable({},{__index = function (t,k)

				local _,callpoint = pcall(function() error("",4) end)

				print(string.format(msg,string.gsub(callpoint,"(^w%*%.%w*%:%d+)","%1")))

				return o[k]

			end,

			__newindex = function (t,k,v)

               	local _,callpoint = pcall(function() error("",4) end)

				print(string.format(msg,string.gsub(callpoint,"(^w%*%.%w*%:%d+)","%1")))

				o[k] = v

				return o[k]

			end

		})

	elseif(type(o) == "function") then

		return function(...)

			local _,callpoint = pcall(function() error("",4) end)

			print(string.format(msg,string.gsub(callpoint,"(^w%*%.%w*%:%d+)","%1")))

			return o(unpack(arg))

		end

	end

end

Example Usage:

Ace = {}



function Ace:print(msg)

	print(msg)

end



function foo()

	print("FOO!")

end

ace = deprecate(Ace,"ace","Ace")

FOO = deprecate(foo,"FOO","foo")



FOO()

ace:print("moo")

Output of Example Usage:



./deprecate.lua:38: Warning, deprecated feature 'FOO' in use.  Use 'foo' instead.

FOO!

./deprecate.lua:39: Warning, deprecated feature 'ace' in use.  Use 'Ace' instead.

moo

Lua: Lazy Map Implementation: Round One

kergoth (Chris Larson) — Mon, 05 Dec 2005 16:13:24 GMT

Concept code for a lazy map implementation in Lua

require "std.table" -- For memoize



function map(t, f)

    local nt = table.memoize(function (k) return f(t[k]) end)

    local mt = getmetatable(nt)

    function mt:__pairs()

        local k

        local function mynext()

            k,v = next(t, k)

            if k == nil then return nil end

            return k,nt[k]

        end

        return mynext, self

    end

    return nt

end

Example Usage:

require "std.base" -- For better table tostring()



local mylist = {1,3,5,7,9}

local newlist = map(mylist, function(v) return 3 * v - 2 end)

assert(mylist[3] == 5)

assert(newlist[3] == 13)



require "std.base" -- For the pairs() that obeys the __pairs metamethod

print("old:", mylist)

print("new(3*v-2):", newlist)

Lua: Sane Granular Defaults for User Supplied Data

kergoth (Chris Larson) — Mon, 05 Dec 2005 16:05:04 GMT

This code is an example of how to implement sane defaults for user supplied data in a generically useful fashion. It was written for use in World of Warcraft User Interface addons, though it would be useful elsewhere.

local mooDB



local defaults = {

    a = {

        foo = "bar"

    },

    b = 1,

    c = {

        bar = "foo"

    },

}



if not mooDB then

    -- NOTE: This would not be in the actual real world code.  This

    -- simulates user data, normally loaded from some sort

    -- of datastore, which is SavedVariables in the case of

    -- World of Warcraft.

    mooDB = {

        c = {

            bop = "whee"

        }

    }

end



function inheritdefaults(t, defaults)

    for k,v in pairs(defaults) do

        if t[k] then

            if type(v) == "table" then

                inheritdefaults(t[k], v)

            end

        end

    end



    local mt = getmetatable(t) or {}

    function mt:__index(k)

        return defaults[k]

    end

    return setmetatable(t, mt)

end



inheritdefaults(mooDB, defaults)



assert(mooDB ~= defaults)

assert(mooDB.a == defaults.a)

assert(mooDB.c ~= defaults.c)

assert(mooDB.a.foo == "bar")

assert(mooDB.b == 1)

assert(mooDB.c.bar == "foo")

assert(mooDB.c.bop == "whee")

Lua: Descending Table Traversal Round 2: Iterator Object

kergoth (Chris Larson) — Mon, 05 Dec 2005 13:27:31 GMT

This is some concept code I threw together for Lua to see how feasable it was to make a lua object/table into an iterator that you can manipulate. This iterator descends through all tables and subtables of any queued table. It returns the "path" we're at, as a string, the current table, the key, and the value.

Code:

traverse = {}

function traverse:new(tname)

	local o = {}

	o.names = {}

	o.queue = {}

	o.cur = {

		tbl = nil,

		path = nil,

		state = nil,

	}



	local mt = {}

	function mt:__call(tn)

		return o:iter(tn)

	end

	mt.__index = self

	setmetatable(o, mt)



	if tname then

		o:enqueue(tname)

	end

	return o

end

function traverse:next()

	local v

	local names, queue, cur = self.names, self.queue, self.cur



	local function _poptbl()

		if cur.tbl then

			names[cur.tbl] = nil

		end

		cur.tbl = table.remove(queue, 1)

		cur.path = names[cur.tbl]

		cur.state = nil

	end



	repeat

		-- Find something to return to the user...

		if not cur.state then

			-- Pop a new table off the stack

			_poptbl()

			if not cur.tbl then

				-- No more tables to process

				return nil

			end

		end

		cur.state,v = next(cur.tbl, cur.state)

	until cur.state



	if type(v) == "table" then

		local path = cur.path.."."..cur.state

		names[v] = path

		table.insert(queue, v)

	end

	return cur.path,cur.tbl,cur.state,v

end

function traverse:iter(tname)

	if tname then

		self:enqueue(tname)

	end

	return function(...) return self:next(unpack(arg)) end, nil, nil

end

function traverse:enqueue(tname)

	local v = _G[tname]

	table.insert(self.queue, v)

	self.names[v] = tname

end

function traverse:reset()

	self.names = {}

	self.queue = {}

end

local traverse_mt = {

    __call = function(self, tname)

             	if tname then

             		return self:new(tname):iter()

             	else

             		return self:new()

             	end

             end

}

setmetatable(traverse, traverse_mt)

Example Usage:

foo = {a={},b={},c={"bar"},d={e={},f={"moo"}},1,2,3,4,5}

bar = {"alpha", "beta", "theta", omega = {}}



local mytraverser = traverse()

mytraverser:enqueue("bar")

mytraverser:enqueue("foo")

for p,t,k,v in mytraverser() do

--for p,t,k,v in traverse('foo') do

	print(string.format("%s[%s] = %s",tostring(p),tostring(k),tostring(v)))

end

Output from Example Usage:

bar[1] = alpha

bar[2] = beta

bar[3] = theta

bar[omega] = table: 0x510650

foo[1] = 1

foo[2] = 2

foo[3] = 3

foo[4] = 4

foo[5] = 5

foo[a] = table: 0x5102d0

foo[c] = table: 0x510370

foo[b] = table: 0x510320

foo[d] = table: 0x5103c0

foo.c[1] = bar

foo.d[e] = table: 0x5104c0

foo.d[f] = table: 0x510510

foo.d.f[1] = moo