Merge commit '83bef6955e014d40c0f00db9cebe09113154e999'

docs/content/en/functions/default.md

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+---
+title: default
+description: Allows setting a default value that can be returned if a first value is not set.
+qref: "Returns a default value if a value is not set when checked."
+godocref:
+date: 2017-02-01
+publishdate: 2017-02-01
+lastmod: 2017-02-01
+keywords: [defaults]
+categories: [functions]
+menu:
+  docs:
+    parent: "functions"
+toc:
+signature: ["default DEFAULT INPUT"]
+workson: []
+hugoversion:
+relatedfuncs: []
+deprecated: false
+draft: false
+aliases: [/functions/default/]
+needsexamples: false
+---
+
+`default` checks whether a given value is set and returns a default value if it is not. *Set* in this context means different things depending on date type:
+
+* non-zero for numeric types and times
+* non-zero length for strings, arrays, slices, and maps
+* any boolean or struct value
+* non-nil for any other types
+
+`default` function examples reference the following content page:
+
+{{< code file="content/posts/default-function-example.md" >}}
+---
+title: Sane Defaults
+seo_title:
+date: 2017-02-18
+font:
+oldparam: The default function helps make your templating DRYer.
+newparam:
+---
+{{< /code >}}
+
+`default` can be written in more than one way:
+
+```
+{{ index .Params "font" | default "Roboto" }}
+{{ default "Roboto" (index .Params "font") }}
+```
+
+Both of the above `default` function calls return `Roboto`.
+
+A `default` value, however, does not need to be hard coded like the previous example. The `default` value can be a variable or pulled directly from the front matter using dot notation:
+
+{{< code file="variable-as-default-value.html" nocopy="true" >}}
+{{$old := .Params.oldparam }}
+<p>{{ .Params.newparam | default $old }}</p>
+{{< /code >}}
+
+Which would return:
+
+```
+<p>The default function helps make your templating DRYer.</p>
+```
+
+And then using dot notation
+
+{{< code file="dot-notation-default-value.html" >}}
+<title>{{ .Params.seo_title | default .Title }}</title>
+{{< /code >}}
+
+Which would return
+
+{{< output file="dot-notation-default-return-value.html" >}}
+<title>Sane Defaults</title>
+{{< /output >}}
+
+The following have equivalent return values but are far less terse. This demonstrates the utility of `default`:
+
+Using `if`:
+
+{{< code file="if-instead-of-default.html" nocopy="true" >}}
+<title>{{if .Params.seo_title}}{{.Params.seo_title}}{{else}}{{.Title}}{{end}}</title>
+=> Sane Defaults
+{{< /code >}}
+
+Using `with`:
+
+{{< code file="with-instead-of-default.html" nocopy="true" >}}
+<title>{{with .Params.seo_title}}{{.}}{{else}}{{.Title}}{{end}}</title>
+=> Sane Defaults
+{{< /code >}}