Editing Module:Arguments/doc (section)

=== 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 <code>valueFunc</code> option. The input to this option must be a function that takes two parameters, <code>key</code> and <code>value</code>, and returns a single value. This value is what you will get when you access the field <code>key</code> in the <code>args</code> table.

Example 1: this function preserves whitespace for the first positional argument, but trims all other arguments and removes all other blank arguments.
<syntaxhighlight lang="lua">
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
})
</syntaxhighlight>

Example 2: this function removes blank arguments and converts all arguments to lower case, but doesn't trim whitespace from positional parameters.
<syntaxhighlight lang="lua">
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
})
</syntaxhighlight>

Note: the above functions will fail if passed input that is not of type <code>string</code> or <code>nil</code>. This might be the case if you use the <code>getArgs</code> 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 <code>p.main</code> and <code>p._main</code> functions, or something similar).

Example 1:
<syntaxhighlight lang="lua">
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
})
</syntaxhighlight>

Example 2:
<syntaxhighlight lang="lua">
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
})
</syntaxhighlight>

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