arguments

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It is a meta-module, meant for use by other modules, and should not be called from #invoke directly. Its features include:

Easy trimming of arguments and removal of blank arguments.
Arguments can be passed by both the current frame and by the parent frame at the same time. (More details below.)
Arguments can be passed in directly from another Lua module or from the debug console.
Arguments are fetched as needed, which can help avoid (some) problems with ... tags.
Most features can be customized.

Basic use

First, you need to load the module. It contains one function, named getArgs.

local getArgs = require('Module:Arguments').getArgs

In the most basic scenario, you can use getArgs inside your main function. The variable args is a table containing the arguments from #invoke. (See below for details.)

local getArgs = require('Module:Arguments').getArgs local p = {}  function p.main(frame) local args = getArgs(frame) -- Main module code goes here. end  return p

However, the recommended practice is to use a function just for processing arguments from #invoke. This means that if someone calls your module from another Lua module you don't have to have a frame object available, which improves performance.

local getArgs = require('Module:Arguments').getArgs local p = {}  function p.main(frame) local args = getArgs(frame) return p._main(args) end  function p._main(args) -- Main module code goes here. end  return p

If you want multiple functions to use the arguments, and you also want them to be accessible from #invoke, you can use a wrapper function.

local getArgs = require('Module:Arguments').getArgs  local function makeInvokeFunc(funcName) return function (frame) local args = getArgs(frame) return p[funcName](args) end end  local p = {}  p.func1 = makeInvokeFunc('_func1')  function p._func1(args) -- Code for the first function goes here. end  p.func2 = makeInvokeFunc('_func2')  function p._func2(args) -- Code for the second function goes here. end  return p

Options

The following options are available. They are explained in the sections below.

local args = getArgs(frame, { trim = false, removeBlanks = false, valueFunc = function (key, value) -- Code for processing one argument end, frameOnly = true, parentOnly = true, parentFirst = true, readOnly = true, noOverwrite = true })

Trimming and removing blanks

Blank arguments often trip up coders new to converting MediaWiki templates to Lua. In template syntax, blank strings and strings consisting only of whitespace are considered false. However, in Lua, blank strings and strings consisting of whitespace are considered true. This means that if you don't pay attention to such arguments when you write your Lua modules, you might treat something as true that should actually be treated as false. To avoid this, by default this module removes all blank arguments.

Similarly, whitespace can cause problems when dealing with positional arguments. Although whitespace is trimmed for named arguments coming from #invoke, it is preserved for positional arguments. Most of the time this additional whitespace is not desired, so this module trims it off by default.

However, sometimes you want to use blank arguments as input, and sometimes you want to keep additional whitespace. This can be necessary to convert some templates exactly as they were written. If you want to do this, you can set the trim and removeBlanks arguments to false.

local args = getArgs(frame, { trim = false, removeBlanks = false })

Custom formatting of arguments

Sometimes you want to remove some blank arguments but not others, or perhaps you might want to put all of the positional arguments in lower case. To do things like this you can use the valueFunc option. The input to this option must be a function that takes two parameters, key and value, and returns a single value. This value is what you will get when you access the field key in the args table.

Example 1: this function preserves whitespace for the first positional argument, but trims all other arguments and removes all other blank arguments.

local args = getArgs(frame, { valueFunc = function (key, value) if key == 1 then return value elseif value then value = mw.text.trim(value) if value ~= '' then return value end end return nil end })

Example 2: this function removes blank arguments and converts all arguments to lower case, but doesn't trim whitespace from positional parameters.

local args = getArgs(frame, { valueFunc = function (key, value) if not value then return nil end value = mw.ustring.lower(value) if mw.ustring.find(value, '%S') then return value end return nil end })

Note: the above functions will fail if passed input that is not of type string or nil. This might be the case if you use the getArgs function in the main function of your module, and that function is called by another Lua module. In this case, you will need to check the type of your input. This is not a problem if you are using a function specially for arguments from #invoke (i.e. you have p.main and p._main functions, or something similar).

Also, please note that the valueFunc function is called more or less every time an argument is requested from the args table, so if you care about performance you should make sure you aren't doing anything inefficient with your code.

Frames and parent frames

Arguments in the args table can be passed from the current frame or from its parent frame at the same time. To understand what this means, it is easiest to give an example. Let's say that we have a module called Module:ExampleArgs. This module prints the first two positional arguments that it is passed.

Module:ExampleArgs is then called by Template:ExampleArgs, which contains the code {{#invoke:ExampleArgs|main|firstInvokeArg}}. This produces the result "firstInvokeArg".

Now if we were to call Template:ExampleArgs, the following would happen:

Code	Result
`{{ExampleArgs}}`	firstInvokeArg
`{{ExampleArgs\|firstTemplateArg}}`	firstInvokeArg
`{{ExampleArgs\|firstTemplateArg\|secondTemplateArg}}`	firstInvokeArg secondTemplateArg

There are three options you can set to change this behaviour: frameOnly, parentOnly and parentFirst. If you set frameOnly then only arguments passed from the current frame will be accepted; if you set parentOnly then only arguments passed from the parent frame will be accepted; and if you set parentFirst then arguments will be passed from both the current and parent frames, but the parent frame will have priority over the current frame. Here are the results in terms of Template:ExampleArgs:

frameOnly

Code	Result
`{{ExampleArgs}}`	firstInvokeArg
`{{ExampleArgs\|firstTemplateArg}}`	firstInvokeArg
`{{ExampleArgs\|firstTemplateArg\|secondTemplateArg}}`	firstInvokeArg

parentOnly

Code	Result
`{{ExampleArgs}}`
`{{ExampleArgs\|firstTemplateArg}}`	firstTemplateArg
`{{ExampleArgs\|firstTemplateArg\|secondTemplateArg}}`	firstTemplateArg secondTemplateArg

parentFirst

Code	Result
`{{ExampleArgs}}`	firstInvokeArg
`{{ExampleArgs\|firstTemplateArg}}`	firstTemplateArg
`{{ExampleArgs\|firstTemplateArg\|secondTemplateArg}}`	firstTemplateArg secondTemplateArg

Note: if you set both the frameOnly and parentOnly options, the module won't fetch any arguments at all from #invoke. This is probably not what you want.

Writing to the args table

Sometimes it can be useful to write new values to the args table. This is possible with the default settings of this module. (However, bear in mind that it is usually better coding style to create a new table with your new values and copy arguments from the args table as needed.)

args.foo = 'some value'

It is possible to alter this behaviour with the readOnly and noOverwrite options. If readOnly is set then it is not possible to write any values to the args table at all. If noOverwrite is set, then it is possible to add new values to the table, but it is not possible to add a value if it would overwrite any arguments that are passed from #invoke.

Ref tags

This module uses metatables to fetch arguments from #invoke. This allows access to both the frame arguments and the parent frame arguments without using the pairs() function. This can help if your module might be passed ... tags as input.

As soon as ... tags are accessed from Lua, they are processed by the MediaWiki software and the reference will appear in the reference list at the bottom of the article. If your module proceeds to omit the reference tag from the output, you will end up with a phantom reference - a reference that appears in the reference list, but no number that links to it. This has been a problem with modules that use pairs() to detect whether to use the arguments from the frame or the parent frame, as those modules automatically process every available argument.

This module solves this problem by allowing access to both frame and parent frame arguments, while still only fetching those arguments when it is necessary. The problem will still occur if you use pairs(args) elsewhere in your module, however.

Known limitations

The use of metatables also has its downsides. Most of the normal Lua table tools won't work properly on the args table, including the # operator, the next() function, and the functions in the table library. If using these is important for your module, you should use your own argument processing function instead of this module.

-- This module provides easy processing of arguments passed to Scribunto from -- #invoke. It is intended for use by other Lua modules, and should not be -- called from #invoke directly.   local libraryUtil = require('libraryUtil') local checkType = libraryUtil.checkType   local arguments = {}   -- Generate four different tidyVal functions, so that we don't have to check the -- options every time we call it.   local function tidyValDefault(key, val) if type(val) == 'string' then val = val:match('^%s*(.-)%s*$') if val == '' then return nil else return val end else return val end end   local function tidyValTrimOnly(key, val) if type(val) == 'string' then return val:match('^%s*(.-)%s*$') else return val end end   local function tidyValRemoveBlanksOnly(key, val) if type(val) == 'string' then if val:find('%S') then return val else return nil end else return val end end   local function tidyValNoChange(key, val) return val end   function arguments.getArgs(frame, options) checkType('getArgs', 1, frame, 'table', true) checkType('getArgs', 2, options, 'table', true) frame = frame or {} options = options or {}   --[[ -- Get the argument tables. If we were passed a valid frame object, get the -- frame arguments (fargs) and the parent frame arguments (pargs), depending -- on the options set and on the parent frame's availability. If we weren't -- passed a valid frame object, we are being called from another Lua module -- or from the debug console, so assume that we were passed a table of args -- directly, and assign it to a new variable (luaArgs). --]] local fargs, pargs, luaArgs if type(frame.args) == 'table' and type(frame.getParent) == 'function' then if options.wrappers then --[[ -- The wrappers option makes Module:Arguments look up arguments in -- either the frame argument table or the parent argument table, but -- not both. This means that users can use either the #invoke syntax -- or a wrapper template without the loss of performance associated -- with looking arguments up in both the frame and the parent frame. -- Module:Arguments will look up arguments in the parent frame -- if it finds the parent frame's title in options.wrapper; -- otherwise it will look up arguments in the frame object passed -- to getArgs. --]] local parent = frame:getParent() if not parent then fargs = frame.args else local title = parent:getTitle():gsub('/sandbox$', '') local found = false if type(options.wrappers) == 'table' then for _,v in pairs(options.wrappers) do if v == title then found = true break end end elseif options.wrappers == title then found = true end if found then pargs = parent.args else fargs = frame.args end end else -- options.wrapper isn't set, so check the other options. if not options.parentOnly then fargs = frame.args end if not options.frameOnly then local parent = frame:getParent() pargs = parent and parent.args or nil end if options.parentFirst then fargs, pargs = pargs, fargs end end else luaArgs = frame 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   --[[ -- Generate the tidyVal function. If it has been specified by the user, we -- use that; if not, we choose one of four functions depending on the -- options chosen. This is so that we don't have to call the options table -- every time the function is called. --]] local tidyVal = options.valueFunc if tidyVal then if type(tidyVal) ~= 'function' then error( "bad value assigned to option 'valueFunc'" .. '(function expected, got ' .. type(tidyVal) .. ')', 2 ) end elseif options.trim ~= false then if options.removeBlanks ~= false then tidyVal = tidyValDefault else tidyVal = tidyValTrimOnly end else if options.removeBlanks ~= false then tidyVal = tidyValRemoveBlanksOnly else tidyVal = tidyValNoChange 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) --[[ -- Accepts multiple tables as input and merges their keys and values -- into one table using the specified iterator. If a value is already -- present it is not overwritten; tables listed earlier have precedence. -- We are also memoizing nil values, but those values can be -- overwritten. --]] for _, t in ipairs(tables) do for key, val in iterator(t) do if metaArgs[key] == nil then local tidiedVal = tidyVal(key, val) if tidiedVal == nil then nilArgs[key] = true else metaArgs[key] = tidiedVal end end end end end   --[[ -- Define metatable behaviour. Arguments are memoized in the metaArgs table, -- and are only fetched from the argument tables once. Fetching arguments -- from the argument tables is the most resource-intensive step in this -- 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 -- in the metatable of when pairs and ipairs have been called, so we do not -- 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 -- the arguments will already have been copied over. --]]   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] if val ~= nil then return val elseif metatable.donePairs or nilArgs[key] then return nil end for _, argTable in ipairs(argTables) do local argTableVal = tidyVal(key, argTable[key]) if argTableVal == nil then nilArgs[key] = true else metaArgs[key] = argTableVal return argTableVal end end return nil end   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 error( 'could not write to argument table key "' .. tostring(key) .. '"; the table is read-only', 2 ) elseif options.noOverwrite and args[key] ~= nil then error( 'could not write to argument table key "' .. tostring(key) .. '"; overwriting existing arguments is not permitted', 2 ) elseif val == nil then --[[ -- 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 else metaArgs[key] = val end end   metatable.__pairs = function () -- Called when pairs is run on the args table. if not metatable.donePairs then mergeArgs(pairs, argTables) metatable.donePairs = true metatable.doneIpairs = true end return pairs(metaArgs) end   metatable.__ipairs = function () -- Called when ipairs is run on the args table. if not metatable.doneIpairs then mergeArgs(ipairs, argTables) metatable.doneIpairs = true end return ipairs(metaArgs) end   return args end   return arguments