Module:Arguments: Difference between revisions

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fix undefined next() behaviour bug by checking for metatable.donePairs in the __index metamethod; also, format the module so it fits into 80 characters
memoize nils using a separate nilArgs table; this fixes a bug where nil values were being iterated over with pairs()
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local arguments = {}
local arguments = {}

local nilArg = {} -- Used for memoizing nil arguments in metaArgs.


-- Generate four different tidyVal functions, so that we don't have to check the
-- Generate four different tidyVal functions, so that we don't have to check the
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luaArgs = frame
luaArgs = frame
end
end

-- Set up the args and metaArgs tables. args will be the one accessed from
-- Set the order of precedence of the argument tables. If the variables are
-- functions, and metaArgs will hold the actual arguments. The metatable
-- nil, nothing will be added to the table, which is how we avoid clashes
-- connects the two together.
-- between the frame/parent args and the Lua args.
local args, metaArgs, metatable = {}, {}, {}
local argTables = {fargs}
⚫
argTables[#argTables + 1] = pargs
⚫
setmetatable(args, metatable)
⚫
argTables[#argTables + 1] = luaArgs


--[[
--[[
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end
end
end
end

--[[
-- Set up the args, metaArgs and nilArgs tables. args will be the one
-- accessed from functions, and metaArgs will hold the actual arguments. Nil
-- arguments are memoized in nilArgs, and the metatable connects all of them
-- together.
⚫
--]]
local args, metaArgs, nilArgs, metatable = {}, {}, {}, {}
⚫
setmetatable(args, metatable)


local function mergeArgs(iterator, tables)
local function mergeArgs(iterator, tables)
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for _, t in ipairs(tables) do
for _, t in ipairs(tables) do
for key, val in iterator(t) do
for key, val in iterator(t) do
local metaArgsVal = metaArgs[key]
if metaArgs[key] == nil then
if metaArgsVal == nil or metaArgsVal == nilArg then
local tidiedVal = tidyVal(key, val)
local tidiedVal = tidyVal(key, val)
if tidiedVal == nil then
if tidiedVal == nil then
metaArgs[key] = nilArg
nilArgs[key] = true
else
else
metaArgs[key] = tidiedVal
metaArgs[key] = tidiedVal
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end
end
end
end

-- Set the order of precedence of the argument tables. If the variables are
-- nil, nothing will be added to the table, which is how we avoid clashes
-- between the frame/parent args and the Lua args.
local argTables = {fargs}
⚫
argTables[#argTables + 1] = pargs
⚫
argTables[#argTables + 1] = luaArgs


--[[
--[[
-- Define metatable behaviour. Arguments are memoized in the metaArgs table,
-- Define metatable behaviour. Arguments are memoized in the metaArgs table,
-- and are only fetched from the argument tables once. Nil arguments are
-- and are only fetched from the argument tables once. Fetching arguments
-- from the argument tables is the most resource-intensive step in this
-- also memoized using the nilArg variable in order to increase performance.
-- Also, we keep a record in the metatable of when pairs and ipairs have
-- module, so we try and avoid it where possible. For this reason, nil
-- arguments are also memoized, in the nilArgs table. Also, we keep a record
-- been called, so we do not run pairs and ipairs on fargs and pargs more
-- than once. We also do not run ipairs on fargs and pargs if pairs has
-- in the metatable of when pairs and ipairs have been called, so we do not
-- already been run, as all the arguments will already have been copied
-- run pairs and ipairs on the argument tables more than once. We also do
-- not run ipairs on fargs and pargs if pairs has already been run, as all
-- over.
-- the arguments will already have been copied over.
--]]
--]]


metatable.__index = function (t, key)
metatable.__index = function (t, key)
--[[
-- Fetches an argument when the args table is indexed. First we check
-- to see if the value is memoized, and if not we try and fetch it from
-- the argument tables. When we check memoization, we need to check
-- metaArgs before nilArgs, as both can be non-nil at the same time.
-- If the argument is not present in metaArgs, we also check whether
-- pairs has been run yet. If pairs has already been run, we return nil.
-- This is because all the arguments will have already been copied into
-- metaArgs by the mergeArgs function, meaning that any other arguments
-- must be nil.
--]]
local val = metaArgs[key]
local val = metaArgs[key]
if metatable.donePairs or val ~= nil then
if val ~= nil then
--[[
return val
elseif metatable.donePairs or nilArgs[key] then
-- We have either memoized the argument already, or pairs has been
⚫
return nil
-- called, meaning that mergeArgs has already copied all of the
-- available arguments into the metaArgs table. We need to check for
-- pairs as we can't memoize nils to the metaArgs table while pairs
-- is iterating. Adding new instances of nilArg to the metaArgs
-- table while pairs is iterating over it produces undefined
-- behaviour in the next() function.
⚫
--]]
if val == nilArg then
⚫
return nil
⚫
else
return val
⚫
end
end
end
for _, argTable in ipairs(argTables) do
for _, argTable in ipairs(argTables) do
local argTableVal = tidyVal(key, argTable[key])
local argTableVal = tidyVal(key, argTable[key])
if argTableVal == nil then
if argTableVal == nil then
metaArgs[key] = nilArg
nilArgs[key] = true
else
else
metaArgs[key] = argTableVal
metaArgs[key] = argTableVal
Line 186: Line 187:


metatable.__newindex = function (t, key, val)
metatable.__newindex = function (t, key, val)
-- This function is called when a module tries to add a new value to the
-- args table, or tries to change an existing value.
if options.readOnly then
if options.readOnly then
error(
error(
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)
)
elseif val == nil then
elseif val == nil then
⚫
--[[
⚫
metaArgs[key] = nilArg -- Memoize nils.
-- If the argument is to be overwritten with nil, we need to erase
-- the value in metaArgs, so that __index, __pairs and __ipairs do
-- not use a previous existing value, if present; and we also need
-- to memoize the nil in nilArgs, so that the value isn't looked
-- up in the argument tables if it is accessed again.
⚫
--]]
metaArgs[key] = nil
⚫
nilArgs[key] = true -- Memoize nils.
else
else
metaArgs[key] = val
metaArgs[key] = val
Line 208: Line 219:


metatable.__pairs = function ()
metatable.__pairs = function ()
-- Called when pairs is run on the args table.
if not metatable.donePairs then
if not metatable.donePairs then
mergeArgs(pairs, argTables)
mergeArgs(pairs, argTables)
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metatable.doneIpairs = true
metatable.doneIpairs = true
end
end
return function (t, k)
return pairs(metaArgs)
local nk, val = next(metaArgs, k)
if val == nilArg then
⚫
val = nil
end
return nk, val
end
end
end


metatable.__ipairs = function ()
metatable.__ipairs = function ()
-- Called when ipairs is run on the args table.
if not metatable.doneIpairs then
if not metatable.doneIpairs then
mergeArgs(ipairs, argTables)
mergeArgs(ipairs, argTables)
metatable.doneIpairs = true
metatable.doneIpairs = true
end
end
return function (t, i)
return ipairs(metaArgs)
local val = metaArgs[i + 1]
if val == nil then
return nil
elseif val == nilArg then
val = nil
end
return i + 1, val
end, nil, 0
end
end


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