Modulus:parameters/doc

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Purpose

This module provides processing and checking of template arguments.

process

process(args, params, return_unknown)

Processes arguments with a given list of parameters, and returns a table containing the processed arguments. The args parameter specifies the arguments to be processed; they are the arguments you might retrieve from frame:getParent().args. The params parameter specifies a list of valid parameters, and consists of a table. If an argument is encountered that is not in the parameter table, an error is shown.

The parameters table should have the parameter names as the indexes, and a (possibly empty) table of parameter tags as the value. An empty table as the value merely states that the parameter exists, but should not receive any special treatment. Possible parameter tags are listed below.

An example parameters table (from Module:translations):

{
	[1] = {required = true, default = "und"},
	[2] = {},
	[3] = {list = true},
	["alt"] = {},
	["sc"] = {},
	["tr"] = {},
}

The return_unknown parameter, if set to true, prevents the function from triggering an error when it comes across an argument with a name that it doesn't recognise. Instead, the return value is a pair of values: the first is the processed arguments as usual, while the second contains all the unrecognised arguments that were left unprocessed. This allows you to do multi-stage processing, where the entire set of arguments that a template should accept is not known at once. For example, an inflection-table might do some generic processing on some arguments, but then defer processing of the remainder to the function that handles a specific inflectional type.

Parameter tags

required = true

The parameter is required; an error is shown if it is not present. The template's page itself is an exception; no error is shown there.

default =

Specifies a default value for the parameter, if it is absent or empty. When used on list parameters, this specifies a default value for the first item in the list only. Note that it is not possible to generate a default that depends on the value of other parameters.

If used together with required = true, the default applies only to the template's page itself. This can be used to show an example text.

alias_of =

Treat the parameter as an alias of another. When arguments are specified for this parameter, they will automatically be renamed and stored under the alias name. This allows for parameters with multiple alternative names, while still treating them as if they had only one name. It is even possible for the alias_of = to have a name that is not a parameter itself.

Aliases should not be required, as this prevents the other name or names of the parameter from being used. Parameters that are aliases and required at the same time are tracked (see Special:WhatLinksHere/Template:tracking/parameters/required alias).

allow_empty = true

If the argument is an empty string value, it is not converted to nil, but kept as-is.

allow_whitespace = true

Spacing characters such as spaces and newlines at the beginning and end of a positional parameter are not removed.

type =

Specifies what value type to convert the argument into. The default is to leave it as a text string. Alternatives are:

type = "boolean"

The value is treated as a boolean value, either true or false. No value, the empty string, and the strings "0", "no", "n" and "false" are treated as false, all other values are considered true.

type = "number"

The value is converted into a number, or nil if the value is not parsable as a number.

list =

Treat the parameter as a list of values, each having its own parameter name, rather than a single value. The parameters will have a number at the end, except optionally for the first (but see also require_index = true). For example, list = true on a parameter named "head" will include the parameters |head= (or |head1=), |head2=, |head3= and so on. If the parameter name is a number, another number doesn't get appended, but the counting simply continues, e.g. for parameter 3 the sequence is |3=, |4=, |5= etc. List parameters are returned as numbered lists, so for a template that is given the parameters |head=a|head2=b|head3=c, the processed value of the parameter "head" will be { "a", "b", "c" }.

The value for list = can also be a string. This tells the module that parameters other than the first should have a different name, which is useful when the first parameter in a list is a number, but the remainder is named. An example would be for genders: list = "g" on a parameter named 1 would have parameters |1=, |g2=, |g3= etc.

If the number is not located at the end, it can be specified by putting an equal sign "=" at the number position. For example, parameters |f1accel=, |f2accel=, ... can be captured by using the parameter name "f=accel", as is done in Module:headword/templates.

allow_holes = true

This is used in conjunction with list-type parameters. By default, the values are tightly packed in the resulting list. This means that if, for example, an entry specified head=a|head3=c but not |head2=, the returned list will be {"a", "c"}, with the values stored at the indices 1 and 2, not 1 and 3. If it is desirable to keep the numbering intact, for example if the numbers of several list parameters correlate with each other (like those of {{compound}}), then this tag should be specified.

If allow_holes = true is given, there may be nil values in between two real values, which makes many of Lua's table processing functions no longer work, like # or ipairs(). To remedy this, the resulting table will contain an additional named value, maxindex, which tells you the highest numeric index that is present in the table. In the example above, the resulting table will now be { "a", nil, "c", maxindex = 3}. That way, you can iterate over the values from 1 to maxindex, while skipping nil values in between.

require_index = true

This is used in conjunction with list-type parameters. By default, the first parameter can have its index omitted. For example, a list parameter named head can have its first parameter specified as either |head= or |head1=. If require_index = true is specified, however, only |head1= is recognized, and |head= will be treated as an unknown parameter. {{affixusex}} (and variants {{suffixusex}}, {{prefixusex}}) use this, for example, on all list parameters. One possible use opened up by this is to distinguish between |head= and |head1= as different parameters. This is used in {{affixusex}} and variants, for example, to distinguish between |sc= (a script code for all elements in the usex's language) and |sc1= (the script code of the first element, used when |lang1= is also specified to indicate that the first element is in a different language).