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Improve .Scratch entry (#454)

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* Improve .Scratch entry

* read also
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@ -20,66 +20,94 @@ draft: false
aliases: [/extras/scratch/,/doc/scratch/] aliases: [/extras/scratch/,/doc/scratch/]
--- ---
In most cases you can do well without `Scratch`, but there are some use cases that aren't solvable with Go's templates without `Scratch`'s help, due to scoping issues. In most cases you can do okay without `Scratch`, but due to scoping issues, there are many use cases that aren't solvable in Go Templates without `Scratch`'s help.
{{% note %}} {{% note %}}
See [this Go issue](https://github.com/golang/go/issues/10608) for the main motivation behind Scratch. See [this Go issue](https://github.com/golang/go/issues/10608) for the main motivation behind Scratch.
{{% /note %}} {{% /note %}}
{{% note %}}
For a detailed analysis of `.Scratch` and in context use cases, see this [post](https://regisphilibert.com/blog/2017/04/hugo-scratch-explained-variable/).
{{% /note %}}
## Methods
`Scratch` is added to both `Page` and `Shortcode` -- with following methods: `Scratch` is added to both `Page` and `Shortcode` -- with following methods:
* `Set` and `Add` takes a `key` and the `value` to add. #### .Set
* `Get` returns the `value` for the `key` given. Set the given value to a given key
* `SetInMap` takes a `key`, `mapKey` and `value`
* `GetSortedMapValues` returns array of values from `key` sorted by `mapKey`
* `Delete` takes a `key` to remove
`Set` and `SetInMap` can store values of any type. ```go-html-template
{{ .Scratch.Set "greeting" "Hello" }}
```
#### .Get
Get the value of a given key
```go-html-template
{{ .Scratch.Set "greeting" "Hello" }}
----
{{ .Scratch.Get "greeting" }} > Hello
```
#### .Add
Will add a given value to existing value 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. 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.
```go-html-template
{{ .Scratch.Add "greetings" "Hello" }}
{{ .Scratch.Add "greetings" "Welcome" }}
----
{{ .Scratch.Get "greetings" }} > HelloWelcome
```
```go-html-template
{{ .Scratch.Add "total" 3 }}
{{ .Scratch.Add "total" 7 }}
----
{{ .Scratch.Get "total" }} > 10
```
```go-html-template
{{ .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 add a map of `mapKey` and `value` to the given `key`.
```go-html-template
{{ .Scratch.SetInMap "greetings" "english" "Hello" }}
{{ .Scratch.SetInMap "greetings" "french" "Bonjour" }}
----
{{ .Scratch.Get "greetings" }} > map[french:Bonjour english:Hello]
```
#### .GetSortedMapValues
Returns array of values from `key` sorted by `mapKey`
```go-html-template
{{ .Scratch.SetInMap "greetings" "english" "Hello" }}
{{ .Scratch.SetInMap "greetings" "french" "Bonjour" }}
----
{{ .Scratch.GetSortedMapValues "greetings" }} > [Hello Bonjour]
```
#### .Delete
Removes the given key
```go-html-template
{{ .Scratch.Delete "greetings" }}
```
## Scope
The scope of the backing data is global for the given `Page` or `Shortcode`, and spans partial and shortcode includes. The scope of the backing data is global for the given `Page` or `Shortcode`, and spans partial and shortcode includes.
Note that `.Scratch` from a shortcode will return the shortcode's `Scratch`, which in most cases is what you want. If you want to store it in the page scroped Scratch, then use `.Page.Scratch`. Note that `.Scratch` from a shortcode will return the shortcode's `Scratch`, which in most cases is what you want. If you want to store it in the page scoped Scratch, then use `.Page.Scratch`.
## Sample usage
The usage is best illustrated with some samples:
```
{{ $.Scratch.Add "a1" 12 }}
{{ $.Scratch.Get "a1" }} {{/* => 12 */}}
{{ $.Scratch.Add "a1" 1 }}
{{ $.Scratch.Get "a1" }} // {{/* => 13 */}}
{{ $.Scratch.Add "a2" "AB" }}
{{ $.Scratch.Get "a2" }} {{/* => AB */}}
{{ $.Scratch.Add "a2" "CD" }}
{{ $.Scratch.Get "a2" }} {{/* => ABCD */}}
{{ $.Scratch.Add "l1" (slice "A" "B") }}
{{ $.Scratch.Get "l1" }} {{/* => [A B] */}}
{{ $.Scratch.Add "l1" (slice "C" "D") }}
{{ $.Scratch.Get "l1" }} {{/* => [A B C D] */}}
{{ $.Scratch.Set "v1" 123 }}
{{ $.Scratch.Get "v1" }} {{/* => 123 */}}
{{ $.Scratch.SetInMap "a3" "b" "XX" }}
{{ $.Scratch.SetInMap "a3" "a" "AA" }}
{{ $.Scratch.SetInMap "a3" "c" "CC" }}
{{ $.Scratch.SetInMap "a3" "b" "BB" }}
{{ $.Scratch.GetSortedMapValues "a3" }} {{/* => []interface {}{"AA", "BB", "CC"} */}}
{{ $.Scratch.Add "a" 1 }}
{{ $.Scratch.Delete "a" }}
{{ $.Scratch.Add "a" 2 }}
{{ $.Scratch.Get "a" }} {{/* => 2 */}}
```
{{% note %}}
The examples above uses the special `$` variable, which refers to the top-level node. This is the behavior you most likely want, and will help remove some confusion when using `Scratch` inside page range loops -- and you start inadvertently calling the wrong `Scratch`. But there may be use cases for `{{ .Scratch.Add "key" "some value" }}`.
{{% /note %}}
[pagevars]: /variables/page/ [pagevars]: /variables/page/