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129 lines
3.5 KiB
Markdown
129 lines
3.5 KiB
Markdown
---
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title: .Scratch
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description: Acts as a "scratchpad" to allow for writable page- or shortcode-scoped variables.
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godocref:
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date: 2017-02-01
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publishdate: 2017-02-01
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lastmod: 2017-02-01
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keywords: [iteration]
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categories: [functions]
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menu:
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docs:
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parent: "functions"
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toc:
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signature: []
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workson: []
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hugoversion:
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relatedfuncs: []
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deprecated: false
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draft: false
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aliases: [/extras/scratch/,/doc/scratch/]
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---
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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.
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`.Scratch` is available as methods on `Page` and `Shortcode`. Since Hugo 0.43 you can also create a locally scoped `Scratch` using the template func `newScratch`.
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{{% note %}}
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See [this Go issue](https://github.com/golang/go/issues/10608) for the main motivation behind Scratch.
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{{% /note %}}
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{{% note %}}
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For a detailed analysis of `.Scratch` and in context use cases, see this [post](https://regisphilibert.com/blog/2017/04/hugo-scratch-explained-variable/).
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{{% /note %}}
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## Get a Scratch
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From Hugo `0.43` you can also create a locally scoped `Scratch` by calling `newScratch`:
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```go-html-template
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$scratch := newScratch
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$scratch.Set "greeting" "Hello"
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```
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A `Scratch` is also added to both `Page` and `Shortcode`. `Scratch` has the following methods:
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#### .Set
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Set the given value to a given key
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```go-html-template
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{{ .Scratch.Set "greeting" "Hello" }}
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```
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#### .Get
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Get the value of a given key
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```go-html-template
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{{ .Scratch.Set "greeting" "Hello" }}
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----
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{{ .Scratch.Get "greeting" }} > Hello
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```
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#### .Add
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Will add a given value to existing value of the given key.
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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.
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```go-html-template
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{{ .Scratch.Add "greetings" "Hello" }}
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{{ .Scratch.Add "greetings" "Welcome" }}
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----
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{{ .Scratch.Get "greetings" }} > HelloWelcome
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```
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```go-html-template
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{{ .Scratch.Add "total" 3 }}
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{{ .Scratch.Add "total" 7 }}
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----
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{{ .Scratch.Get "total" }} > 10
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```
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```go-html-template
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{{ .Scratch.Add "greetings" (slice "Hello") }}
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{{ .Scratch.Add "greetings" (slice "Welcome" "Cheers") }}
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----
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{{ .Scratch.Get "greetings" }} > []interface {}{"Hello", "Welcome", "Cheers"}
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```
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#### .SetInMap
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Takes a `key`, `mapKey` and `value` and add a map of `mapKey` and `value` to the given `key`.
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```go-html-template
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{{ .Scratch.SetInMap "greetings" "english" "Hello" }}
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{{ .Scratch.SetInMap "greetings" "french" "Bonjour" }}
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----
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{{ .Scratch.Get "greetings" }} > map[french:Bonjour english:Hello]
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```
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#### .GetSortedMapValues
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Returns array of values from `key` sorted by `mapKey`
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```go-html-template
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{{ .Scratch.SetInMap "greetings" "english" "Hello" }}
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{{ .Scratch.SetInMap "greetings" "french" "Bonjour" }}
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----
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{{ .Scratch.GetSortedMapValues "greetings" }} > [Hello Bonjour]
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```
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#### .Delete
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Removes the given key
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```go-html-template
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{{ .Scratch.Delete "greetings" }}
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```
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#### .Values
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`Values` returns the raw backing map. Note that you should just use this method on the locally scoped `Scratch` instances you obtain via `newScratch`, not
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`.Page.Scratch` etc., as that will lead to concurrency issues.
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## Scope
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The scope of the backing data is global for the given `Page` or `Shortcode`, and spans partial and shortcode includes.
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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`.
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[pagevars]: /variables/page/
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