Help:Substitution/fr

La substitution est une conversion automatique du wikitext d'une page, lorsque la page est enregistrée, dans le cas où le wikitext fait référence à un ou plusieurs modèles, variables ou fonctions Parser (fonctions d'analyseur syntaxique).

Dans le cas de la substitution de modèle, l'appel de modèle est remplacé par le contenu du modèle avec substitution des paramètres. Ainsi, un modèle est utilisé comme macro et la page est macro expansée lorsque la page est enregistrée plutôt que, comme cela se produit habituellement, lorsque la page est vue.

En cas de substitution d'une variable ou d'une fonction Parser (fonction d'analyseur), la référence à celle-ci est remplacée par la valeur résultante.

La substitution se fait en mettant le mot magique   ou   après les doubles accolades ouvrantes, sans espaces intermédiaires comme dans les exemples :   et  . Le code  est utile dans la substitution multi-niveaux, voir ci-dessous.

Le résultat (sous la forme de la différence avec le wikitext enregistré) peut être vu avant (ou sans) l'enregistrement en appuyant sur « Afficher les modifications ». Cependant, si le texte couvre plus d'un paragraphe, cette page de différence n'est pas très adaptée pour copier le résultat (par exemple pour une substitution pas à pas sans enregistrer chaque étape), à cause des signes plus dans la marge.

Applications
Substitution d'un modèle :


 * Rendre une page rendue indépendante du modèle :
 * La page rendue ne change pas lorsque le modèle est modifié.
 * La page peut être copiée sur un autre wiki MediaWiki sans copier le modèle.
 * Facilitez le rendu des pages et donc plus rapidement pour le serveur
 * Analysez et démontrez le fonctionnement des modèles. Cependant, dans certains cas, la substitution fonctionne différemment.
 * Faire la correspondance entre wikitext et page rendue plus facile à comprendre (cela peut s'appliquer, l'inverse peut également s'appliquer).

Substitution d'une variable dépendante du temps :


 * Créez une page rendue indépendante de l'heure.

Substitution d'une variable dépendante de la page :


 * Rendre une page rendue indépendante du changement de nom de la page et de la copie du wikitext sur une autre page (le contraire s'applique si la variable PAGENAME est utilisée dans une partie non incluse de la page pour inclure la page elle-même).

Certaines extensions MediaWiki ont la restriction que si elles sont utilisées dans un modèle avec des paramètres, elles ne fonctionnent que si le modèle est remplacé.

Vue d'ensemble
Pour la discussion de substitution, un modèle ordinaire est la page à laquelle il est fait référence, soit dans l'étiquette {&#123;subst:pagename &#160; &#125;} (pour les pages dans l'espace de noms du modèle), soit {&#123;subst:fullpagename &#160; &#125;} (pour les pages dans d'autres espaces de noms). Un modèle prédéfini est une variable ou une fonction parser (fonction d'analyseur syntaxique) qui est substitué de manière similaire.

La substitution est un processus distinct qui est effectué avant l'expansion de tout modèle, fonction d'analyse syntaxique, variable ou paramètre non substitué.

Un appel de substitution peut contenir d'autres appels de substitution. De même, le modèle de substitution d'une substitution peut contenir d'autres appels de substitution. Les substitutions dans l'expression pour le nom du modèle ou de la fonction d'analyseur, dans les définitions de paramètres du modèle ou de la fonction d'analyseur substitué et dans le corps du modèle substitué sont effectuées en premier.

Puisque l'expansion est faite plus tard, toute expression utilisée dans une substitution qui contient des paires d'accolades doubles, aura les accolades traitées comme du texte brut. Ainsi, pendant la substitution, il peut y avoir un nom de paramètre avec des accolades dans l'appel de substitution (par exemple ) qui correspond à un paramètre du même nom dans le corps du modèle (par exemple  ).

Si l'on tente d'appliquer une substitution à un modèle inexistant, etc. il n'y a pas de substitution, le préfixe "subst:" est conservé dans le wikitext.

Après le processus de substitution, l'expansion des modèles, etc. et d'autres traitements du wikitext résultants, fonctionnent comme d'habitude. La substitution étant terminée, cela ne peut pas annuler une incohérence de noms de paramètres qui s'est produite lors de la substitution (voir également la section Substitution partielle ci-dessous).

La substitution n'est possible que si tout ce qui suit a été complètement évalué.


 * nom du modèle, fonction d'analyse ou une variable
 * cas d'un modèle : noms des paramètres dans l'appel du modèle et dans le modèle lui-même
 * cas #if, #ifexpr, #ifexist et #iferror, paramètre après la virgule ','
 * cas #ifeq, paramètre après la virgule ',' et le suivant
 * cas #switch, paramètre après la virgule et les expressions à gauche des signes égale '='

Comme il a été dit, parce que la substitution se fait avant tout autre expansion, l'évaluation nécessaire évoquée ci-avant ne se réalise pas si les expressions comportent une expansion sans substitution.

Egalement dans le cas où il existe d'autres fonctions d'analyse syntaxique que celles indiquées, un paramètre non complètement évalué après la virgule ',' fait que la fonction d'analyse est appliquée au wikicode entre accollades, et non au wikicode expansé, ce qui biaise le résultat.

Exemples :
 * avec, ne realise aucune substitution, parce que Help:L k est une page qui n'existe pas, bien que Help:Lk soit rendu en tant que Help:Lk. Ainsi le wikicode résultant est le même que le wikicode original et il est généré comme.
 * yes avec, donne le wikicode "yes", alors que yes donne le wikicode "no", et est généré comme «  ».

En principe le wikicode résultant de la substitution complète est, immédiatement après cela, généré de la même manière que le wikicode d'une inclusion ordinaire.

Notez néanmoins que lors de la substitution d'une fonction d'analyse syntaxique, une paramètre indéfini avec valeur par défaut, utilisé en tant que valeur de paramètre, n'est pas remplacé par cette valeur (dans la Wikipedia anglophone), et par exemple n'est pas autorisé dans l'expression numérique évaluée lors de la substitution de #expr:
 * donne, alors que donne le message d'erreur de syntaxe suivant « Expression error: unrecognised punctuation character "{" »

Lorsqu'il s'agit de substituer un modèle qui contient cela, est remplacé soit par la valeur de, soit par 3 et n'apporte donc pas de difficulté.

using is rendered as ;  gives the wikitext a rendered the same as the wikitext, and on the next edit/save changed into start-a -middle--end;  gives the wikitext , rendered as. This is because, both without substitution and in the case of full substitution, the pipe characters in template calls, excluding those inside inner template calls, template parameters, links, and image tags, determine the separation of parameter definitions from each other and from the template name. This separation does not depend on possible extra pipe characters in the expanded form of the template name and parameter definitions. However, if after substitution of an inner template the pipe character is in the outer template call it is one like any other and plays its part in determining the separation. In other words, parsing is done first once for substitution, and then once for rendering, but in both cases not an extra time in between. In the case of substitution of the inner template only, two subsequent parsings are effective.

When substituting a template containing (a parameter tag with default) this results in the value of p if it is defined, and otherwise in q. For example, using &lbrace;&lbrace;timc|t pd}} (in English Wikipedia),  gives the wikitext 2.

If a page substitutes itself (e.g. in the noinclude-part of a template page) it substitutes the old version.

Considérations d'utilisation
As mentioned, a change of an ordinary template after substitution does not affect the page in which it was substituted, and a substituted variable depending on time no longer depends on time, etc. However, a substitution of e.g. does not affect rendering at all.

The relationship between wikitext of a page and its rendering can become easier to understand after substitution, because one has all wikitext together, and parameter substitutions have been performed.

It can also become more complex. Separately focusing on understanding a template call and understanding the template content can be easier. Wikitext after substitution is often more complex than when the required wikitext would have been written directly.

Unlike a template call (if one knows about templates), wikitext after substitution does not show how one can produce a similar result. The wikitext can be long and complicated, and therefore cumbersome to write directly, or it can be simple, e.g. a number resulting from a computation, but cumbersome to find directly. When studying the wikitext of a page one may think that this wikitext is what one is supposed to write and find directly to get the result, even in cases where that would be very impractical.

In such cases documentation of the template call is useful. Just like in computer programming we change the source code and/or the data to produce new results, and we do not directly change the object file, here we would change the template calls and/or the templates, instead of changing the wikitext resulting from substitution directly.

Modèles ordinaires
In the case of substituting an ordinary template, the template tag is replaced by the wikitext of the template, with the parameter values substituted for the parameters.


 * Example&#58;, containing
 * and called as   (see tc) gives the wikitext:
 * , rendering as
 * start-a-middle--end.
 * start-a-middle--end.

Substitution removes the noinclude parts and the includeonly tags.

Parameters:
 * A substitution with p=r replaces and  by r; this includes the cases that r is of the form  or.
 * A substitution with undefined p preserves and replaces  by the default q (in English Wikipedia).

With "subst:" the replacement of a template tag by wikitext does not work recursively. For full recursive substitution use Special:ExpandTemplates. See also substall, and multilevel substitution below.

Stepwise substitution of templates including other templates including more templates etc. can be useful for analyzing and documenting the behaviour of complex templates, for an example see m:Template talk:Lop.

However, after a substitution a page may render differently, e.g. if templates produce braces, pipes, and/or equals signs which after substitution determine expansion of other templates, but without substitution are treated as plain text.

In the absence of parameters, template substitution can be compared with copying the wikitext, or the rendering of a previewed or saved {&#123; &#160; pagename &#160; &#125;} inclusion. However, template substitution excludes  parts, removes   tags, and replaces undefined parameters with defaults by those defaults.

Modèles prédéfinis
In the case of substituting a predefined template, without parameters depending on other templates, the tag is replaced by the result.

Note:  has to be added directly in front of the predefined template name without intervening spaces.

Applying subst to a variable works like applying it to a template. E.g. a timestamp:


 * -- T UTC :

may give the wikitext


 * 2010-04-10 T 06:30 UTC

rendered as
 * 2010-04-10 T 06:30 UTC

In the case of substituting a predefined template with a parameter depending on another template, that has to be substituted too, with a separate  modifier, otherwise the result is undefined.


 * gives IN, the same wikitext as is expanded to; UC: is applied to the output "in" of Tc.
 * gives File.
 * gives wikitext     rendered as.
 * gives the wikitext startHelpend (see t1)
 * gives the wikitext start12end
 * gives the wikitext startABCDEFend
 * gives the wikitext 1331
 * gives the wikitext ABCABCABC
 * gives the wikitext 1e-05 (see LC:)
 * gives (at the time of writing) the wikitext 30
 * gives (at the time of writing) the wikitext THURSDAY

However:
 * 1)  gives the wikitext   rendered as.
 * 2)  stays , rendered as  (see ns:).

As mentioned before, on substitution, all calls without substitution of templates, variables, and parser functions are treated as plain text. As a result substitution of the outer  in a nested often is only suitable if all inner  are also substituted.

In the case of substitution of a predefined template, if the expression for one of its parameters contains with undefined p, this code reduces to 3. However, on the page itself, is treated as such, not as 3.

Examples:
 * gives
 * gives
 * gives Expression error: Unrecognized punctuation character &quot;{&quot;.
 * substituting a template containing gives 6 if p is not assigned a value, and twice the number p if it is assigned a value.
 * the same result can be obtained from a template containing, if the substitution call has a parameter of " ".

Compare:
 * 2* gives 2*
 * 2* gives 2*
 * gives the wikitext 2* rendered as 2*

and also (from above):
 * gives IN, just like does; UC is applied to the output "in" of Tc.
 * gives the wikitext  rendered as.

In the substitution of UC, the inclusion tag is treated as string just like.

Substitution partielle
Inside an ordinary template one can apply substitution to an ordinary template call containing a parameter, to replace it by the direct wikitext containing the parameter. It amounts to automatically merging the two templates (creating a "composite template" like a composite function). It is not possible if the inner and/or outer template is predefined. (However, manually merging e.g. a call of #expr inside another one is useful for increasing the accuracy of the result by avoiding intermediate rounding to 12 digits.)

This way one can dispense with the optional substitution technique described below, and apply substitution of the resulting outer template by simply using "subst:" (unless there are more nesting levels).

Example:
 * gives the wikitext start--end, just that of , without noinclude parts and includeonly tags
 * ab gives the wikitext start-ab-end

Examples with double substitution:
 * gives the wikitext start--endstart--endstart--endstart--end
 * gives the wikitext start--endstart--endstart--end

Substitution multi-niveaux
When substituting a template it may be desirable to carry out a substitution inside the template too. This can be done with "safesubst:" in the template. To prevent premature substitution (i.e., when the template is saved), this code is provided as default value of an unused parameter. Since the empty string is a possible—but for other purposes uncommon—parameter name, it is usually a suitable choice for the name of this unused parameter, so we can use the code.

The difference with  is that , evaluating to   if the parameter with the empty string as name is undefined, not only allows multilevel substitution but also multilevel transclusion, because on transclusion it is ignored. To make the template such that it allows the choice between these two options as well as one-level substitution (and more choices if more templates, parser functions and/or variables are involved) one or more parameters are needed, see below.

Sometimes a template call defines a value of the parameter with the empty string as name, just for inserting this value as comment inside the template tag, or for lay-out of the template tag, see template tag lay-out. This would affect the working of the code. To allow this other dummy use of the parameter, another parameter name can be used in, or to avoid any possible clash of dummy parameter names, includeonly tags can be used, see below.

Multilevel substitution with independent control of each substitution separately
A parameter subst (or more, each with its own name) can be used with "safesubst:" and the empty string as possible values. Thus we can for example control whether an inner template is substituted too when the outer template is substituted. Either possibility can be made the default.

Inner templates with parameters may control further inner substitutions in the same way; these parameters may depend on the substitution parameter controlling the substitution of the inner template, since if that is not substituted, inner substitutions within that template are not possible.

Similarly, if there are multiple templates, parser functions, and/or variables in the inner template(s) we can control substitution of all, either independently by using different parameters, or with some or all using the same parameter.

For example, if template T uses parameter subst1:
 * with the empty string as default, T calls inner templates and parser functions prefixing their names with ; for calling T we can use:
 * .. (no substitution)
 * .. (one-level substitution)
 * .. (two-level substitution)
 * .. (ditto)
 * with default "safesubst:", T calls inner templates and parser functions prefixing their names with ; for calling T we can use
 * .. (no substitution)
 * .. (one-level substitution)
 * .. (two-level substitution)

To transfer the choice of substituting or not to templates and parser functions called inside the inner templates of T, we can add to the call of these inner templates something of the form subst2= or subst2= , respectively (parser functions and variables don't get the additional parameter).

See also m:Help:Calculation and.

Partial substitution
Using a template prepared for optional  only with ordinary substitution, without specifying parameter values, allows to insert its code into another template, like copy and paste, but all parts and  keywords automatically stripped. Executing inserted code instead of calling it may be more efficient for the server.

A typical example for this technique is expanding, within another template, a template used as test expression in a #switch: like : parameter tag case 0 etc. parameter tag case 0 etc. parameter tag case 0 etc. m:Template:len is prepared for optional substitution, therefore both solutions work, but the latter solution substituting its code is simpler and more efficient.
 * 1) Development code:
 * 1) Standard solution:
 * 1) Better solution: create template code by applying substitution using this wikitext:

See m:Template:csn and m:Template:lz12 for cases where Template:len was substituted in this way.

If a template uses a parameter whose name is an expression containing a template or parser function, and the template is called with a corresponding parameter definition (in terms of the final name of the parameter) it expands properly only if at the time of expansion of the template the expression for the name of the parameter is or has been evaluated. Thus if the template is substituted without substituting the expression for the parameter name, the parameter definition is "lost", so the parameter becomes undefined. Therefore in such a case no substitution can give the same rendered result as full substitution, while partial substitution gives a different result. See e.g..

Composite operations
By a template A is called with, as parameter, a call of template B with a parameter p. We could integrate such template calls to a single call  of a "composite template" C with parameter p.


 * The wikitext for template C would be, or with optional substitution the following construct&#58;
 * {&#123; &#160;{&#123;{subst }&#125;}&#160; A|{&#123; &#160;{&#123;{subst  }&#125;}&#160; B| &#160;|subst={&#123;{subst  }&#125;}&#160; &#125;} &#160;|subst={&#123;{subst  }&#125;}&#160; &#125;}
 * The subst=  is only necessary for recursive substitution as explained above.

Note that it is not useful to specify " subst: " since in the substitution phase this tag does not reduce to the default "subst:".

If A and/or B is predefined the construct is similar, but without subst= for that template.

Includeonly
An alternative method to prevent premature substitution, known as "includeonly subst magic", is with a pair of includeonly tags. Substitution is prevented by having the template call inside these tags. Substitution is also prevented by having one or both tags anywhere in the template call except inside a parameter definition. Thus the tag(s) can be before, inside, or after "safesubst:" or "subst:", or inside or after the template name. The positions of the two tags only influence the rendering of the template page itself.

The form {&#123; something&#125;} suggests that substitution is prevented by discarding "safesubst:" on the page itself, but actually substitution is prevented because the safesubst-syntax is disturbed by the tags.

It doesn't substitute "something" at the time of the creation of the relevant template, but has the desired effect when the template is substituted.

For examples see "preload" in Extension:InputBox and "substitution" in Help:Magic words.

Creating a page which applies substitution on the next save
See m:Help:Recursive conversion of wikitext.

Forced substitution
Some templates deliberately refuse to work without substitution, for an example see Conv-dist. This technique is essential for templates like prod producing some kind of timestamp, e.g. adding pages to dated categories.


 * The following code in any template T outputs a warning unless recursive substitution with  is in effect&#58;
 * Output for {&#123;T&#125;} or {&#123;subst:T&#125;}&#58; Warning,
 * output for {&#123;T|subst=subst:&#125;}&#58; ,
 * output for {&#123;subst:T|subst=subst:&#125;}&#58; nothing (no remaining wikitext).
 * output for {&#123;subst:T|subst=subst:&#125;}&#58; nothing (no remaining wikitext).


 * This is a rare case where replacing ifdef by #if: doesn't work directly.

Substitution of part of the parameters
Let template A use parameters 1 and 2. Consider creating a template B with one parameter 1, corresponding to A, with a given value q of parameter 2. Compare and. They look the same on the template page, see e.g., but the first does not work because is treated as text, not as parameter.

However, with substitution (using "subst:" or Special:Expandtemplates) the resulting wikitext is the same, without distinction between a text and a parameter, it is a parameter anyway, so "1=" is not needed.

If A contains e.g. #expr with an expression containing both parameters the same applies, except that we can only substitute the highest level (A), not the parser function, so we cannot use Special:Expandtemplates.

In general, substituting a parameter and applying a template or parser function sometimes gives the same result as substituting the template or parser function with the triple-braced parameter code and then substituting the parameter.

Without defaults (all rendered the same in one-step substitution as without substitution):

Examples with equality:
 * A template containing pqr substituted with 1=u, 2=v gives puqvr; substituted with 2=v it gives pqvr, which itself, substituted with 1=u gives also puqvr.
 * Two-level substitution of a template containing with 3=u, 4=v gives up; substituted with 4=v it gives p, which itself, substituted with 3=u gives up.

Examples without equality:
 * Two-level substitution of a template containing with 3=, 4=v gives the empty string; substituted with 4=v it gives vp, which itself, substituted with 3=u remains vp.
 * Two-level substitution of a template containing with 1=u, 2=v gives up; substituted with 2=v it gives pp (the bug), which itself, substituted with 3=u, gives upp.
 * Two-level substitution of a template containing with 1=7, 2=8 gives 56; substituted with 2=8 it gives &lt;strong class="error">Expression error: Unrecognised punctuation character "{"&lt;/strong>, which itself, substituted with 1=7, remains the same.

Thus without equality we may or may not get an error message.

One example shows that substitution of one parameter can be affected by the bug mentioned above. However, we can then replace e.g. by  and do full substitution, except that substvoid is undefined, preventing the bug. The result works already correctly with transclusion. Subsequently it can be substituted with substvoid=subst: so that we get the plain.

With defaults:

Rendered the same as without substitution:
 * Two-level substitution of a template containing pqr with 2=v gives pqvr.
 * Two-level substitution of a template containing with 4=v gives p.

Not rendered the same as without substitution:
 * Two-level substitution of a template containing with 4=v gives vp.
 * Two-level substitution of a template containing with 2=v gives pp (the bug).
 * Two-level substitution of a template containing with 2=8 gives &lt;strong class="error">Expression error: Unrecognised punctuation character "{"&lt;/strong>.

After substitution with the parameter definition:
 * vp gives vp.
 * p gives pp (the bug).
 * gives &lt;strong class="error">Expression error: Unrecognised punctuation character "{"&lt;/strong>.

Rewritten:
 * gives the empty string.
 * p gives dp.
 * gives 48.

Limitations
Substitution is not available inside  and  tags. If you write, it is not substituted nor transcluded, but remains as-is.

Documenter la substitution
Usage of a template through  does not automatically show up in page histories. Therefore providing the line of wikitext containing "subst:" in the edit summary is especially useful.

Also pages with a substituted template do not show up in backlinks, and the template does not appear in the list of transcluded templates on the edit page. The template could add pages to a category to track substitutions, but listing this category on a page may clutter the list of content-based categories the page is in. Also, comments outside noinclude tags are included in the wikitext. Thus a comment can be used to mention the template. It can even contain the values of the parameters, because substitution of parameters works even in comments.

Voir aussi

 * Help:Substitution/tl;dr – tl;dr
 * w:Help:Substitution
 * w:Wikipedia:Template substitution – partly technical, partly policy
 * T4003 – feature request to allow marking a template as being substituted without "subst:"
 * Templates containing a call to itself with "subst:" and producing a similar call with updated info, either replacing or adding to the previous info: