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    Farthest Frontier

    This module provides easy processing of arguments passed from #invoke. 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.
    • Most features can be customized.

    Basic use[edit source]

    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
    

    Recommended practice[edit source]

    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
    

    The way this is called from a template is {{#invoke:Example|main}} (optionally with some parameters like {{#invoke:Example|main|arg1=value1|arg2=value2}}), and the way this is called from a module is require('Module:Example')._main({arg1 = 'value1', arg2 = value2, 'spaced arg3' = 'value3'}). What this second one does is construct a table with the arguments in it, then gives that table to the p._main(args) function, which uses it natively.

    Multiple functions[edit source]

    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 p = {}
    
    local function makeInvokeFunc(funcName)
    	return function (frame)
    		local args = getArgs(frame)
    		return p[funcName](args)
    	end
    end
    
    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[edit source]

    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,
    	wrappers = {
    		'Template:A wrapper template',
    		'Template:Another wrapper template'
    	},
    	readOnly = true,
    	noOverwrite = true
    })
    

    Trimming and removing blanks[edit source]

    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[edit source]

    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).

    Examples 1 and 2 with type checking

    Example 1:

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

    Example 2:

    local args = getArgs(frame, {
    	valueFunc = function (key, value)
    		if type(value) == 'string' then
    			value = mw.ustring.lower(value)
    			if mw.ustring.find(value, '%S') then
    				return value
    			else
    				return nil
    			end
    		else
    			return value
    		end
    	end
    })
    

    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[edit source]

    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 code
    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)
    	local first = args[1] or ''
    	local second = args[2] or ''
    	return first .. ' ' .. second
    end
    
    return p
    

    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

    Notes:

    1. 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.
    2. In some situations a parent frame may not be available, e.g. if getArgs is passed the parent frame rather than the current frame. In this case, only the frame arguments will be used (unless parentOnly is set, in which case no arguments will be used) and the parentFirst and frameOnly options will have no effect.

    Wrappers[edit source]

    The wrappers option is used to specify a limited number of templates as wrapper templates, that is, templates whose only purpose is to call a module. If the module detects that it is being called from a wrapper template, it will only check for arguments in the parent frame; otherwise it will only check for arguments in the frame passed to getArgs. This allows modules to be called by either #invoke or through a wrapper template without the loss of performance associated with having to check both the frame and the parent frame for each argument lookup.

    For example, the only content of Template:Side box (excluding content in <noinclude>...</noinclude> tags) is {{#invoke:Side box|main}}. There is no point in checking the arguments passed directly to the #invoke statement for this template, as no arguments will ever be specified there. We can avoid checking arguments passed to #invoke by using the parentOnly option, but if we do this then #invoke will not work from other pages either. If this were the case, the |text=Some text in the code {{#invoke:Side box|main|text=Some text}} would be ignored completely, no matter what page it was used from. By using the wrappers option to specify 'Template:Side box' as a wrapper, we can make {{#invoke:Side box|main|text=Some text}} work from most pages, while still not requiring that the module check for arguments on the Template:Side box page itself.

    Wrappers can be specified either as a string, or as an array of strings.

    local args = getArgs(frame, {
    	wrappers = 'Template:Wrapper template'
    })
    


    local args = getArgs(frame, {
    	wrappers = {
    		'Template:Wrapper 1',
    		'Template:Wrapper 2',
    		-- Any number of wrapper templates can be added here.
    	}
    })
    

    Notes:

    1. The module will automatically detect if it is being called from a wrapper template's /sandbox subpage, so there is no need to specify sandbox pages explicitly.
    2. The wrappers option effectively changes the default of the frameOnly and parentOnly options. If, for example, parentOnly were explicitly set to 0 with wrappers set, calls via wrapper templates would result in both frame and parent arguments being loaded, though calls not via wrapper templates would result in only frame arguments being loaded.
    3. If the wrappers option is set and no parent frame is available, the module will always get the arguments from the frame passed to getArgs.

    Writing to the args table[edit source]

    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[edit source]

    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 <ref>...</ref> tags as input.

    As soon as <ref>...</ref> 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 without any number linking 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[edit source]

    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
    
    local function matchesTitle(given, title)
    	local tp = type( given )
    	return (tp == 'string' or tp == 'number') and mw.title.new( given ).prefixedText == title
    end
    
    local translate_mt = { __index = function(t, k) return k end }
    
    function arguments.getArgs(frame, options)
    	checkType('getArgs', 1, frame, 'table', true)
    	checkType('getArgs', 2, options, 'table', true)
    	frame = frame or {}
    	options = options or {}
    
    	--[[
    	-- Set up argument translation.
    	--]]
    	options.translate = options.translate or {}
    	if getmetatable(options.translate) == nil then
    		setmetatable(options.translate, translate_mt)
    	end
    	if options.backtranslate == nil then
    		options.backtranslate = {}
    		for k,v in pairs(options.translate) do
    			options.backtranslate[v] = k
    		end
    	end
    	if options.backtranslate and getmetatable(options.backtranslate) == nil then
    		setmetatable(options.backtranslate, {
    			__index = function(t, k)
    				if options.translate[k] ~= k then
    					return nil
    				else
    					return k
    				end
    			end
    		})
    	end
    
    	--[[
    	-- 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 matchesTitle(options.wrappers, title) then
    					found = true
    				elseif type(options.wrappers) == 'table' then
    					for _,v in pairs(options.wrappers) do
    						if matchesTitle(v, title) then
    							found = true
    							break
    						end
    					end
    				end
    
    				-- We test for false specifically here so that nil (the default) acts like true.
    				if found or options.frameOnly == false then
    					pargs = parent.args
    				end
    				if not found or options.parentOnly == false then
    					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
    		end
    		if options.parentFirst then
    			fargs, pargs = pargs, fargs
    		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(tables)
    		--[[
    		-- Accepts multiple tables as input and merges their keys and values
    		-- into one table. If a value is already present it is not overwritten;
    		-- tables listed earlier have precedence. We are also memoizing nil
    		-- values, which can be overwritten if they are 's' (soft).
    		--]]
    		for _, t in ipairs(tables) do
    			for key, val in pairs(t) do
    				if metaArgs[key] == nil and nilArgs[key] ~= 'h' then
    					local tidiedVal = tidyVal(key, val)
    					if tidiedVal == nil then
    						nilArgs[key] = 's'
    					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.
    		--]]
    		if type(key) == 'string' then
    			key = options.translate[key]
    		end
    		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
    				metaArgs[key] = argTableVal
    				return argTableVal
    			end
    		end
    		nilArgs[key] = 'h'
    		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 type(key) == 'string' then
    			key = options.translate[key]
    		end
    		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] = 'h'
    		else
    			metaArgs[key] = val
    		end
    	end
    
    	local function translatenext(invariant)
    		local k, v = next(invariant.t, invariant.k)
    		invariant.k = k
    		if k == nil then
    			return nil
    		elseif type(k) ~= 'string' or not options.backtranslate then
    			return k, v
    		else
    			local backtranslate = options.backtranslate[k]
    			if backtranslate == nil then
    				-- Skip this one. This is a tail call, so this won't cause stack overflow
    				return translatenext(invariant)
    			else
    				return backtranslate, v
    			end
    		end
    	end
    
    	metatable.__pairs = function ()
    		-- Called when pairs is run on the args table.
    		if not metatable.donePairs then
    			mergeArgs(argTables)
    			metatable.donePairs = true
    		end
    		return translatenext, { t = metaArgs }
    	end
    
    	local function inext(t, i)
    		-- This uses our __index metamethod
    		local v = t[i + 1]
    		if v ~= nil then
    			return i + 1, v
    		end
    	end
    
    	metatable.__ipairs = function (t)
    		-- Called when ipairs is run on the args table.
    		return inext, t, 0
    	end
    
    	return args
    end
    
    return arguments
    
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