View source for User:BrandonXLF/Help:Infinite parameters

{{Wikipedia how to|H:INF|WP:INFPARAM}}

Support for '''infinite parameters''' allows a template to accept a unlimited number of parameters. These can either be unnamed [[H:PARAMETERS|parameters]] ({{Para|1}}, {{Para|2}}, {{Para|3}}, etc.) or named ({{Para|item1}}, {{Para|item2}}, {{Para|item3}}, etc.). This is similar in concept to a [[variadic function]]. As [[H:WT|wikitext]] does not have built-in support for infinite parameters, templates that support infinite parameters make use of [[WP:LUA|Lua modules]].

== Custom modules ==
One way add support for infinite parameters to a template is to write a custom [[WP:LUA|Lua modules]] that implements the template. This is done by modules like [[Module:Jct]], [[Module:Infobox]], [[Module:List]], and [[Module:Template link general]]. There are several strategies for supporting infinite parameters in Lua, some of which are demonstrated below.

=== Sequential parameters ===

==== Using [[mw:Extension:Scribunto/Lua_reference_manual#ipairs|<code>ipairs</code>]] ====
[[mw:Extension:Scribunto/Lua_reference_manual#ipairs|<code>ipairs</code>]] is a built in function that can be used to iterate over sequential numbered (unnamed) parameters. It works by reading non-<code>nil</code> values starting with the key <code>1</code>. It is used in conjunction with a [[mw:Extension:Scribunto/Lua_reference_manual#for|for loop]]. For example, if a module, <code>__MODULE__</code>, existed with the code below:<syntaxhighlight lang="lua">
local p = {}

function p.main(frame)
    local args = frame:getParent().args
    local out = ''

    for i, v in ipairs(args) do
        if out then out = out .. ', ' end
        out = out .. i .. ' is ' .. v
    end

    return out
end

return p
</syntaxhighlight>

Then, when a template with <code><nowiki>{{#invoke:__MODULE__|main}}</nowiki></code> is called with <code><nowiki>{{__TEMPLATE__|A|B|C}}</nowiki></code>, the output <code>1 is A, 2 is B, 3 is C</code> would be produced.

==== Using [[mw:Extension:Scribunto/Lua_reference_manual#while|while]] ====

Using a [[mw:Extension:Scribunto/Lua_reference_manual#while|while loop]] works great when there is a prefix in front of the parameter number as [[mw:Extension:Scribunto/Lua_reference_manual#ipairs|ipairs]] will not work in those situations. The definition of <code>i</code> can also be set to start with a different number besides <code>1</code>.  For example, if a module, <code>__MODULE__</code>, existed with the code below:<syntaxhighlight lang="lua">
local p = {}

function p.main(frame)
    local args = frame:getParent().args
    local out = ''
    local i = 1

    while args['prefix' .. i] do
        if out then out = out .. ', ' end
        out = out .. 'prefix' .. i .. ' is ' .. v
        i = i + 1
    end

    return out
end

return p
</syntaxhighlight>

Then, when a template with <code><nowiki>{{#invoke:__MODULE__|main}}</nowiki></code> is called with <code><nowiki>{{__TEMPLATE__|prefix1=A|prefix2=B|prefix3=c}}</nowiki></code>, the output <code>1 is A, 2 is B, 3 is C</code> would be produced.

=== Non-sequential parameters ===

==== Using [[Module:TableTools#sparseIpairs|<code>TableTools.sparseIpairs</code>]] ====
There are several templates like {{Tl|Infobox}} that need to support non-sequential parameters. This is commonly achieved with [[Module:TableTools]], which contains functions like <code>sparseIpairs</code> for working with sparse arrays. The example below can skip over <code>nil</code> values, whereas the <code>ipairs</code> example stops at the first <code>nil</code> value. For example, if a module, <code>__MODULE__</code>, existed with the code below:<syntaxhighlight lang="lua">local TableTools = require('Module:TableTools')
local p = {}

function p.main(frame)
    local args = frame:getParent().args
    local out = ''

    for i, v in TableTools.sparseIpairs(args) do
        if out then out = out .. ', ' end
        out = out .. i .. ' is ' .. v
    end

    return out
end

return p</syntaxhighlight>Then, when a a template with <code><nowiki>{{#invoke:__MODULE__|main}}</nowiki></code> is called with <code><nowiki>{{__TEMPLATE__|A|B|100=C}}</nowiki></code>, the output <code>1 is A, 2 is B, 100 is C</code> would be produced despite parameters <code>3</code> to <code>99</code> not being defined.

==== Using [[mw:Extension:Scribunto/Lua_reference_manual#pairs|<code>pairs</code>]] and [[mw:Extension:Scribunto/Lua_reference_manual#table.sort|<code>table.sort</code>]] ====
When an existing method like those in [[Module:TableTools]] don't work (due to having prefixed parameter names or other issues), iterating over all arguments with [[mw:Extension:Scribunto/Lua_reference_manual#pairs|<code>pairs</code>]], recording the number of the ones you're interested in, sorting the array of said numbers with [[mw:Extension:Scribunto/Lua_reference_manual#table.sort|<code>table.sort</code>]], and then using [[mw:Extension:Scribunto/Lua_reference_manual#ipairs|<code>ipairs</code>]] to go over that sorted array is a common method as shown below. For example, if a module, <code>__MODULE__</code>, existed with the code below:<syntaxhighlight lang="lua">
local p = {}

function p.main(frame)
    local args = frame:getParent().args
    local out = ''

    -- Traverse all arguments and record item argument numbers
    local argNums = {}
    for k, _ in pairs(args) do
	    local num = tostring(k):match('^item([1-9]%d*)$')
		if num then table.insert(argNums, tonumber(num)) end
    end

    table.sort(argNums) -- Sort the found argument numbers
    
    for _, num in ipairs(argNums) do
        if out then out = out .. ', ' end
        out = out .. 'item' .. num .. ' is ' .. args['item' .. num]
    end

    return out
end

return p
</syntaxhighlight>Then, when a template with <code><nowiki>{{#invoke:__MODULE__|main}}</nowiki></code> is called with <code><nowiki>{{__TEMPLATE__|item1=A|item2=B|item100=C}}</nowiki></code>, the output <code>item1 is A, item2 is B, item100 is C</code> would be produced despite parameters <code>item3</code> to <code>item99</code> not being defined.

== Using metamodules ==
If you'd like to avoid writing an entire Lua module, there are [[:Category:Template metamodules|metamodules]] that exist to help aid in adding infinite parameter support for functions. Examples on how to use some of these metamodules are shown below.

=== Arbitrary wikitext ===
These modules work by taking wikitext in {{Tag|nowiki}} and expanding it while passing it the appropriate parameters. Examples of using the various modules that support arbitrary wikitext are shown below.

==== Unnamed parameters ====
===== [[Module:Map params]] =====
If the template <code>__TEMPLATE__</code> is defined with the code below:<syntaxhighlight lang="wikitext">{{#invoke:Map params|map|sep=<br>|<nowiki><code>{{{i}}}</code> is {{2x|{{{1}}}|, }}</nowiki>}}</syntaxhighlight>Then,
{|
| <syntaxhighlight lang="wikitext">{{__TEMPLATE__|A|B|C}}</syntaxhighlight>
| would produce
| {{Call wikitext|sourceCode=<nowiki>{{#invoke:Sandbox/BrandonXLF/Module:Map params|map|sep=<br>|<nowiki><code>{{{i}}}</code> is {{2x|{{{1}}}|, }}&lt;/nowiki>}}</nowiki>|A|B|C}}
|}

===== [[Module:ArgRest]] =====
If the template <code>__TEMPLATE__</code> is defined with the code below:<syntaxhighlight lang="wikitext">{{#if:{{{1|}}}|<code>1</code> is {{2x|{{{1}}}|, }}}}{{#invoke:ArgRest|main|<nowiki><br><code>?</code> is {{2x|{{{2}}}|, }}</nowiki>|2}}</syntaxhighlight>Then,
{|
| <syntaxhighlight lang="wikitext">{{__TEMPLATE__|A|B|C}}</syntaxhighlight>
| would produce
| {{Call wikitext|sourceCode=<nowiki>
{{#if:{{{1|}}}|<code>1</code> is {{2x|{{{1}}}|, }}}}{{#invoke:ArgRest|main|<nowiki><br><code>?</code> is {{2x|{{{2}}}|, }}&lt;/nowiki>|2}}</nowiki>|A|B|C}}
|}

===== [[Module:Params]] =====
If the template <code>__TEMPLATE__</code> is defined with the code below:<syntaxhighlight lang="wikitext">{{#invoke:Params|setting|i|<br>|sequential|for_each|<code>$#</code> is {{2x|$@|, }}}}</syntaxhighlight>Then,
{|
| <syntaxhighlight lang="wikitext">{{__TEMPLATE__|A|B|C}}</syntaxhighlight>
| would produce
| {{Call wikitext|sourceCode=<nowiki>{{#invoke:params|setting|i|<br>|sequential|for_each|<code>$#</code> is {{2x|$@|, }}}}</nowiki>|A|B|C}}
|}
Note that this example processes the wikitext before the arguments are substituted. So, the call to {{Tl|2x}} actually outputs <code>$@, $@</code> rather than <code>A, A</code> etc.

==== Named parameters ====
===== [[Module:Map params]] =====
If the template <code>__TEMPLATE__</code> is defined with the code below:<syntaxhighlight lang="wikitext">{{#invoke:Map params|map|prefix=item|extra=extra(i)|sep=<br>|<nowiki><code>item{{{i}}}</code> is {{{item}}}{{#if:{{{extra|}}}|{{sp}}and <code>extra{{{i}}}</code> is {{{extra}}}}}</nowiki>}}</syntaxhighlight>Then,
{|
| <syntaxhighlight lang="wikitext">{{__TEMPLATE__
| item1 = A
| extra1 = Apple
| item2 = B
| extra2 = Orange
| item3 = C
}}</syntaxhighlight>
| would produce
| {{Call wikitext|sourceCode=<nowiki>{{#invoke:Sandbox/BrandonXLF/Module:Map params|map|prefix=item|extra=extra(i)|sep=<br>|<nowiki><code>item{{{i}}}</code> is {{{item}}}{{#if:{{{extra|}}}|{{sp}}and <code>extra{{{i}}}</code> is {{{extra}}}}}&lt;/nowiki>}}</nowiki>|item1=A|extra1=Apple|item2=B|extra2=Orange|item3=C}}
|}

===== [[Module:ArgRest]] =====
If the template <code>__TEMPLATE__</code> is defined with the code below:<syntaxhighlight lang="wikitext">{{#if:{{{item1|}}}|<code>item1</code> is {{{item1}}}{{#if:{{{extra1|}}}|{{sp}}and <code>extra1</code> is {{{extra1}}}}}}}{{#invoke:ArgRest|main|<nowiki><br><code>item?</code> is {{{item2}}}{{#if:{{{extra2|}}}|{{sp}}and <code>extra?</code> is {{{extra2}}}}}</nowiki>|item2}}</syntaxhighlight>Then,
{|
| <syntaxhighlight lang="wikitext">{{__TEMPLATE__
| item1 = A
| extra1 = Apple
| item2 = B
| extra2 = Orange
| item3 = C
}}</syntaxhighlight>
| would produce
| {{Call wikitext|sourceCode=<nowiki>{{#if:{{{item1|}}}|<code>item1</code> is {{{item1}}}{{#if:{{{extra1|}}}|{{sp}}and <code>extra1</code> is {{{extra1}}}}}}}{{#invoke:ArgRest|main|<nowiki><br><code>item?</code> is {{{item2}}}{{#if:{{{extra1|}}}|{{sp}}and <code>extra?</code> is {{{extra2}}}}}&lt;/nowiki>|item2}}</nowiki>|item1=A|extra1=Apple|item2=B|extra2=Orange|item3=C}}
|}

===== [[Module:Params]] =====
If the template <code>__TEMPLATE__</code> is defined with the code below:<syntaxhighlight lang="wikitext">{{#invoke:params|setting|i|<br>|all_sorted|call_for_each_group|__CHILD_TEMPLATE__}}</syntaxhighlight>

And the template <code>__CHILD_TEMPLATE__</code> is defined with the code below:<syntaxhighlight lang="wikitext"><code>item?</code> is {{{item}}}{{#if:{{{extra|}}}|{{sp}} and <code>extra?</code> is {{{extra}}}}}</syntaxhighlight>Then,
{|
| <syntaxhighlight lang="wikitext">{{__TEMPLATE__
| item1 = A
| extra1 = Apple
| item2 = B
| extra2 = Orange
| item3 = C
}}</syntaxhighlight>
| would produce
| {{Call wikitext|sourceCode=<nowiki>{{#invoke:params|setting|i|<br>|all_sorted|call_for_each_group|User:BrandonXLF/Help:Infinite parameters/prefix/child}}</nowiki>|item1=A|extra1=Apple|item2=B|extra2=Orange|item3=C}}
|}
Unlike the other examples, this one uses a child template. This allows the wikitext to be written outside of {{Tag|nowiki}} tags, but it separates the code across multiple templates.

=== Fixed output format ===
These modules are more specialized and limited than the ones above. Examples for using them are below.

==== Unnamed parameters ====
===== [[Module:Separated entries]] =====
If the template <code>__TEMPLATE__</code> is defined with the code below:<syntaxhighlight lang="wikitext">{{#invoke:Separated entries|main|separator=&#32;also&#32;|conjunction=&#32;and finally&#32;}}</syntaxhighlight>Then,
{|
| <syntaxhighlight lang="wikitext">{{__TEMPLATE__|A|B|C}}</syntaxhighlight>
| would produce
| {{Call wikitext|sourceCode=<nowiki>{{#invoke:Separated entries|main|separator=&#32;also&#32;|conjunction=&#32;and finally&#32;}}</nowiki>|A|B|C}}
|}

===== [[Module:Enumerate]] =====
If the template <code>__TEMPLATE__</code> is defined with the code below:<syntaxhighlight lang="wikitext">{{#invoke:Enumerate|main}}</syntaxhighlight>Then,
{|
| <syntaxhighlight lang="wikitext">{{__TEMPLATE__|A|B|C}}</syntaxhighlight>
| would produce
| {{Call wikitext|sourceCode=<nowiki>{{#invoke:Enumerate|main}}</nowiki>|A|B|C}}
|}

==== Named parameters ====
===== [[Module:Enumerate]] =====
If the template <code>__TEMPLATE__</code> is defined with the code below:<syntaxhighlight lang="wikitext">{{#invoke:Enumerate|main|item}}</syntaxhighlight>Then,
{|
| <syntaxhighlight lang="wikitext">{{__TEMPLATE__|item1=A|item2=B|item3=C}}</syntaxhighlight>
| would produce
| {{Call wikitext|sourceCode=<nowiki>{{#invoke:Enumerate|main}}</nowiki>|A|B|C}}
|}

== See also ==
* {{Cl|Template metamodules}}