hugo/content/en/functions/scratch.md

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.Scratch	Acts as a "scratchpad" to store and manipulate data.	iteration	functions	docs parent functions				/extras/scratch/ /doc/scratch/

Scratch is a Hugo feature designed to conveniently manipulate data in a Go Template world. It is either a Page or Shortcode method for which the resulting data will be attached to the given context, or it can live as a unique instance stored in a variable.

{{% note %}} Note that Scratch was initially created as a workaround for a Go template scoping limitation that affected Hugo versions prior to 0.48. For a detailed analysis of .Scratch and contextual use cases, see this blog post. {{% /note %}}

Contexted .Scratch vs. local newScratch

Since Hugo 0.43, there are two different ways of using Scratch:

The Page's .Scratch

.Scratch is available as a Page method or a Shortcode method and attaches the "scratched" data to the given page. Either a Page or a Shortcode context is required to use .Scratch.

{{ .Scratch.Set "greeting" "bonjour" }}
{{ range .Pages }}
  {{ .Scratch.Set "greeting" (print "bonjour" .Title) }}
{{ end }}

The local newScratch

A Scratch instance can also be assigned to any variable using the newScratch function. In this case, no Page or Shortcode context is required and the scope of the scratch is only local. The methods detailed below are available from the variable the Scratch instance was assigned to.

{{ $data := newScratch }}
{{ $data.Set "greeting" "hola" }}

Methods

A Scratch has the following methods:

{{% note %}} Note that the following examples assume a local Scratch instance has been stored in $scratch. {{% /note %}}

.Set

Set the value of a given key.

{{ $scratch.Set "greeting" "Hello" }}

.Get

Get the value of a given key.

{{ $scratch.Set "greeting" "Hello" }}
----
{{ $scratch.Get "greeting" }} > Hello

.Add

Add a given value to existing value(s) of the given key.

For single values, Add accepts values that support Go's + operator. If the first Add for a key is an array or slice, the following adds will be appended to that list.

{{ $scratch.Add "greetings" "Hello" }}
{{ $scratch.Add "greetings" "Welcome" }}
----
{{ $scratch.Get "greetings" }} > HelloWelcome

{{ $scratch.Add "total" 3 }}
{{ $scratch.Add "total" 7 }}
----
{{ $scratch.Get "total" }} > 10

{{ $scratch.Add "greetings" (slice "Hello") }}
{{ $scratch.Add "greetings" (slice "Welcome" "Cheers") }}
----
{{ $scratch.Get "greetings" }} > []interface {}{"Hello", "Welcome", "Cheers"}

.SetInMap

Takes a key, mapKey and value and adds a map of mapKey and value to the given key.

{{ $scratch.SetInMap "greetings" "english" "Hello" }}
{{ $scratch.SetInMap "greetings" "french" "Bonjour" }}
----
{{ $scratch.Get "greetings" }} > map[french:Bonjour english:Hello]

.DeleteInMap

Takes a key and mapKey and removes the map of mapKey from the given key.

{{ .Scratch.SetInMap "greetings" "english" "Hello" }}
{{ .Scratch.SetInMap "greetings" "french" "Bonjour" }}
----
{{ .Scratch.DeleteInMap "greetings" "english" }}
----
{{ .Scratch.Get "greetings" }} > map[french:Bonjour]

.GetSortedMapValues

Return an array of values from key sorted by mapKey.

{{ $scratch.SetInMap "greetings" "english" "Hello" }}
{{ $scratch.SetInMap "greetings" "french" "Bonjour" }}
----
{{ $scratch.GetSortedMapValues "greetings" }} > [Hello Bonjour]

.Delete

Remove the given key.

{{ $scratch.Set "greeting" "Hello" }}
----
{{ $scratch.Delete "greeting" }}

.Values

Return the raw backing map. Note that you should only use this method on the locally scoped Scratch instances you obtain via newScratch, not .Page.Scratch etc., as that will lead to concurrency issues.