TiddlyWiki5/editions/tw5.com/tiddlers/widgets/SetWidget.tid

caption: set
created: 20131115182700000
modified: 20230720174707977
tags: Widgets
title: SetWidget
type: text/vnd.tiddlywiki

! Introduction

The set variable widget assigns a value to a specified [[variable|Variables]]. The new value of the variable is available to the content within the set variable widget.

! Content and Attributes

The content of the `<$set>` widget is the scope for the value assigned to the variable.

|!Attribute |!Description |
|name |The name of the variable to assign (defaults to "currentTiddler") |
|value |The value to assign to the variable if the <<.attr filter>> attribute is missing or not empty |
|tiddler |<<.from-version "5.1.15">> Optional title of the tiddler from which to read the value |
|subtiddler |<<.from-version "5.1.16">> Optionally specifies the title of a subtiddler within a plugin tiddler identified by the ''tiddler'' attribute |
|field |<<.from-version "5.1.15">> Optional field of the tiddler from which to read the value (only used if ''tiddler'' is used) |
|index |<<.from-version "5.1.15">> Optional index of the tiddler from which to read the value (only used if ''tiddler'' is used) |
|filter |An optional filter to be evaluated and assigned to the variable (see "Filtered List Variable Assignment" below). The variable can be used with the <<.olink enlist>> operator |
|select |<<.from-version "5.1.14">> An optional zero-based index of the item to return from the filter output (see below) |
|emptyValue |The value to assign to the variable if the specified value is missing or empty (see below) |

<<.tip """If the value of your variable is enclosed in double square brackets this might indicate that you are returning a list of values from the filter. To use a single title from the filter output without the double square brackets see ''Filtered Item Variable Assignment'' below.""">>

! Examples

!! Simple Variable Assignment

The simplest way of using set variable widget assigns a string to a variable. The following example assigns a literal string

<<<

<$macrocall $name='wikitext-example-without-html' 
src='<$set name="myVariable" value="Some text">
<$text text=<<myVariable>>/>
</$set>' />

<<<

Both the name and value attributes can be transcluded. For example:

<<<

<$macrocall $name='wikitext-example-without-html' 
src='<$set name=anotherVariable value="myVariable">
  <$set name=<<anotherVariable>> value={{$:/language/DefaultNewTiddlerTitle}}>
    <$text text=<<myVariable>>/>
  </$set>
</$set>' />

<<<

!! Conditional Variable Assignment

This form of the set variable widget chooses one of two specified values according to whether a filter evaluates to an empty list. Here's an example that sets a variable according to whether the current tiddler is called "myMagicTitle":

<<<

<$macrocall $name='wikitext-example-without-html' 
src="""<$set name="myVariable" filter="[all[current]field:title[myMagicTitle]]" value="It's magic" emptyValue="It's not magic">
<$text text=<<myVariable>>/>
</$set>""" />

<<<

!! Filtered List Variable Assignment

This form of the set variable widget evaluates the filter and assigns the result to the variable as a space-separated list (using double square brackets for titles containing spaces).

<<.warning """The [[Title List]] format cannot reliably represent items that contain certain specific character sequences such as `]] `. Thus it should not be used where there is a possibility of such sequences occurring.""">>

<<<

<$macrocall $name='wikitext-example-without-html' 
src='<$set name="myVariable" filter="[tag[HelloThere]]">
<$text text=<<myVariable>>/>
</$set>' />

<<<

!! Filtered Item Variable Assignment Single Element

<<.from-version "5.1.14">> This form of the set variable widget evaluates the filter and assigns the specified result to the variable as a single item (ie, not using double square brackets for titles containing spaces).

<<<

<$macrocall $name='wikitext-example-without-html' 
src='<$set name="myVariable" filter="[tag[HelloThere]]" select="0">
<$text text=<<myVariable>>/>
</$set>'/>

<<<

!! Transcluded Variable Assignment

<<.from-version "5.1.15">> This form of the set variable widget obtains the value to assign to the variable from a value in a tiddler field or index. For example:

<<<

<$macrocall $name='wikitext-example-without-html' 
src='<$set name="myVariable" tiddler="HelloThere" field="list">
<$text text=<<myVariable>>/>
</$set>'/>

<<<

The example above could also be written as `<$set name="myVariable" value={{HelloThere!!list}}>`. The advantage of using the ''tiddler'' attribute is that the tiddler title and field or index can themselves be computed. For example:

<<<

<$macrocall $name='wikitext-example-without-html' 
src='<$set name="myTiddler" value="HelloThere">
  <$set name="myVariable" tiddler=<<myTiddler>> field={{$:/docs/anyField!!field}}>
    <$text text=<<myVariable>>/>
  </$set>
</$set>'/>

<<<

!! Using the Set Widget to Create Global Variables

There are times when it makes sense to use the features of the [[SetWidget]] rather than procedures or functions to create global variables.  This can be accomplished by placing the set variable widget in a tiddler that is tagged [[$:/tags/Global|SystemTag: $:/tags/Global]].  If multiple variables are required, the set variable widget can be nested as shown here:

<<<
<div class="doc-example">

```
<$set name="myGlobalVariable" value="I am global">
    <$set name="myOtherGlobalVariable" value="I am also a global variable.">
    </$set>
</$set>
```
</div>
<<<