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LetWidget

Introduction

New in: 5.2.1 The $let widget allows multiple variables to be set in one operation. In some situations it can result in simpler code than using the more flexible $set widget. It differs from the $vars widget in that variables you're defining may depend on earlier variables defined within the same $let.

Content and Attributes

The content of the $let widget is the scope for the value assigned to the variable.

AttributeDescription
{attributes not starting with $}Each attribute name specifies a variable name. The attribute value is assigned to the variable

Attributes are evaluated in the order they are written. Attributes with the same name are allowed. Each time a duplicate attribute is encountered, it will replace the existing value set by the earlier duplicate.

Examples

Consider a case where you need to set multiple variables, where some depend on the evaluation of others.

Using the $let widget, this situation may be handled in the following way:

\define helloworld() Hello world!

<$let target="MyTiddler" currentTiddler={{{ [<target>prefix[$:/settings/for/]] }}} settings={{!!text}} currentTiddler=<<target>> >
  The settings for <<currentTiddler>> are: <<settings>>
</$let>

In contrast, here is the same example using the $set widget:

<$set name="target" value="MyTiddler" >
<$set name="currentTiddler" value={{{ [<target>prefix[$:/settings/for/]] }}} >
<$set name="settings" value={{!!text}} >
<$set name="currentTiddler" value=<<target>> >
  The settings for <<currentTiddler>> are: <<settings>>
</$set>
</$set>
</$set>
</$set>

Remarks

This widget differs from $vars in the following way:

  • Each variable's definition will be immediately available to all proceeding variables in the same let widget. This differs from vars, in which definitions which depend on some variable will always look to the widget's outer scope for a value.

This widget differs from $set in the following ways:

  • A fallback (also known as "emptyValue") cannot be specified
  • Filters cannot be used to produce a conditional variable assignment
  • Variable names must be literal strings