Module:Arguments/doc

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.
 * 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.

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

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.

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.

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

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  and   arguments to.

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  option. The input to this option must be a function that takes two parameters,  and , and returns a single value. This value is what you will get when you access the field  in the   table.

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

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

Note: the above functions will fail if passed input that is not of type  or. This might be the case if you use the  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  and   functions, or something similar).

Example 1:

Example 2:

Also, please note that the  function is called more or less every time an argument is requested from the   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  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. This module prints the first two positional arguments that it is passed.

is then called by, which contains the code. This produces the result "firstInvokeArg".

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

There are three options you can set to change this behaviour:,   and. If you set  then only arguments passed from the current frame will be accepted; if you set   then only arguments passed from the parent frame will be accepted; and if you set   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 :


 * frameOnly


 * parentOnly


 * parentFirst

Notes:
 * 1) If you set both the   and   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   and   options will have no effect.

Wrappers
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  tags) is. 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 Some text in the code  would be ignored completely, no matter what page it was used from. By using the  option to specify 'Template:Side box' as a wrapper, we can make   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.

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 false 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.

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.)

It is possible to alter this behaviour with the  and   options. If  is set then it is not possible to write any values to the args table at all. If  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  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  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  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   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.

Tests

 * See testcases
 * Diff sandbox code