From 8008675983a8fc592a4994de09552edcb3a53252 Mon Sep 17 00:00:00 2001 From: spf13 Date: Tue, 18 Feb 2014 18:34:51 -0500 Subject: [PATCH] Adding Go Template Tutorial --- docs/content/layout/go-templates.md | 281 ++++++++++++++++++++++++++-- 1 file changed, 269 insertions(+), 12 deletions(-) diff --git a/docs/content/layout/go-templates.md b/docs/content/layout/go-templates.md index 093497cdb..39df738e8 100644 --- a/docs/content/layout/go-templates.md +++ b/docs/content/layout/go-templates.md @@ -1,21 +1,278 @@ --- -title: "Go Templates" +title: "Using Go Templates" date: "2013-07-01" groups: ["layout"] -groups_weight: 80 -draft: true +groups_weight: 15 --- Hugo uses the excellent [golang][] [html/template][gohtmltemplate] library for -its template engine. -It is an extremely lightweight engine that provides a very small amount of -logic. -In our experience that it is just the right amount of logic to be able to -create a good static website. +its template engine. It is an extremely lightweight engine that provides a very +small amount of logic. In our experience that it is just the right amount of +logic to be able to create a good static website. If you have used other +template systems from different languages or frameworks you will find a lot of +similarities in go templates. -This is a brief primer on using go templates. The [golang docs][gohtmltemplate] +This document is a brief primer on using go templates. The [golang docs][gohtmltemplate] provide more details. +## Introduction to Go Templates + +Go templates provide an extremely simple template language. It adheres to the +belief that only the most basic of logic belongs in the template or view layer. +One consequence of this simplicity is that go templates parse very quickly. + +A unique characteristic of go templates is they are content aware. Variables and +content will be sanitized depending on the context of where they are used. More +details can be found in the [golang docs][gohtmltemplate]. + +## Basic Syntax + +Go lang templates are html files with the addition of variables and +functions. + +**Go variables and functions are accessible within {{ }}** + +Accessing a predefined variable "foo": + + {{ foo }} + +**Parameters are separated using spaces** + +Calling the add function with input of 1, 2: + + {{ add 1 2 }} + +**Methods and fields are accessed via dot notation** + +Accessing the Page Parameter "bar" + + {{ .Params.bar }} + +**Parentheses can be used to group items together** + + {{ if or (isset .Params "alt") (isset .Params "caption") }} Caption {{ end }} + + +## Variables + +Each go template has a struct (object) made available to it. In hugo each +template is passed either a page or a node struct depending on which type of +page you are rendering. More details are available on the +[variables](/layout/variables) page. + +A variable is accessed by referencing the variable name. + + {{ .Title }} + +Variables can also be defined and referenced. + + {{ $address := "123 Main St."}} + {{ $address }} + + +## Functions + +Go template ship with a few functions which provide basic functionality. The go +template system also provides a mechanism for applications to extend the +available functions with their own. [Hugo template +functions](/layout/functions) provide some additional functionality we believe +are useful for building websites. Functions are called by using their name +followed by the required parameters separated by spaces. Template +functions cannot be added without recompiling hugo. + +**Example:** + + {{ add 1 2 }} + +## Includes + +When including another template you will pass to it the data it will be +able to access. To pass along the current context please remember to +include a trailing dot. The templates location will always be starting at +the /layout/ directory within Hugo. + +**Example:** + + {{ template "chrome/header.html" . }} + + +## Logic + +Go templates provide the most basic iteration and conditional logic. + +### Iteration + +Just like in go, the go templates make heavy use of range to iterate over +a map, array or slice. The following are different examples of how to use +range. + +**Example 1: Using Context** + + {{ range array }} + {{ . }} + {{ end }} + +**Example 2: Declaring value variable name** + + {{range $element := array}} + {{ $element }} + {{ end }} + +**Example 2: Declaring key and value variable name** + + {{range $index, $element := array}} + {{ $index }} + {{ $element }} + {{ end }} + +### Conditionals + +If, else, with, or, & and provide the framework for handling conditional +logic in Go Templates. Like range, each statement is closed with `end`. +There is not an elseif function. + +Go Templates treat the following values as false: + +* false +* 0 +* any array, slice, map, or string of length zero + +**Example 1: If** + + {{ if isset .Params "title" }}

{{ index .Params "title" }}

{{ end }} + +**Example 2: If -> Else** + + {{ if isset .Params "alt" }} + {{ index .Params "alt" }} + {{else}} + {{ index .Params "caption" }} + {{ end }} + +**Example 3: And & Or** + + {{ if and (or (isset .Params "title") (isset .Params "caption")) (isset .Params "attr")}} + +**Example 4: With** + +An alternative way of writing "if" and then referencing the same value +is to use "with" instead. With rebinds the context `.` within its scope, +and skips the block if the variable is absent. + +The first example above could be simplified as: + + {{ with .Params.title }}

{{ . }}

{{ end }} + +## Pipes + +One of the most powerful components of go templates is the ability to +stack actions one after another. This is done by using pipes. Borrowed +from unix pipes, the concept is simple, each pipeline's output becomes the +input of the following pipe. + +Because of the very simple syntax of go templates, the pipe is essential +to being able to chain together function calls. One limitation of the +pipes is that they only can work with a single value and that value +becomes the last parameter of the next pipeline. + +A few simple examples should help convey how to use the pipe. + +**Example 1 :** + + {{ if eq 1 1 }} Same {{ end }} + +is the same as + + {{ eq 1 1 | if }} Same {{ end }} + +It does look odd to place the if at the end, but it does provide a good +illustration of how to use the pipes. + +**Example 2 :** + + {{ index .Params "disqus_url" | html }} + +Access the page parameter called "disqus_url" and escape the HTML. + +**Example 3 :** + + {{ if or (or (isset .Params "title") (isset .Params "caption")) (isset .Params "attr")}} + Stuff Here + {{ end }} + +Could be rewritten as + + {{ isset .Params "caption" | or isset .Params "title" | or isset .Params "attr" | if }} + Stuff Here + {{ end }} + + +## Context (aka. the dot) + +The most easily overlooked concept to understand about golang templates is that {{ . }} +always refers to the current context. In the top level of your template this +will be the data set made available to it. Inside of a iteration it will have +the value of the current item. When inside of a loop the context has changed. . +will no longer refer to the data available to the entire page. If you need to +access this from within the loop you will likely want to set it to a variable +instead of depending on the context. + +**Example:** + + {{ $title := .Site.Title }} + {{ range .Params.tags }} +
  • {{ . }} - {{ $title }}
    • + {{ end }} + +Notice how once we have entered the loop the value of {{ . }} has changed. We +have defined a variable outside of the loop so we have access to it from within +the loop. + +# Hugo Parameters + +Hugo provides the option of passing values to the template language +through the site configuration (for sitewide values), or through the meta +data of each specific piece of content. You can define any values of any +type (supported by your front matter/config format) and use them however +you want to inside of your templates. + + +## Using Content (page) Parameters + +In each piece of content you can provide variables to be used by the +templates. This happens in the [front matter](/content/front-matter). + +An example of this is used in this documentation site. Most of the pages +benefit from having the table of contents provided. Sometimes the TOC just +doesn't make a lot of sense. We've defined a variable in our front matter +of some pages to turn off the TOC from being displayed. + +Here is the example front matter: + +``` +--- +title: "Permalinks" +date: "2013-11-18" +aliases: + - "/doc/permalinks/" +groups: ["extras"] +groups_weight: 30 +notoc: true +--- +``` + +Here is the corresponding code inside of the template: + + {{ if .Params.notoc }} + {{ else }} +
    + {{ .TableOfContents }} +
    + {{ end }} + + + +## Using Site (config) Parameters In your top-level configuration file (eg, `config.yaml`) you can define site parameters, which are values which will be available to you in chrome. @@ -40,9 +297,9 @@ January 1st, instead of hunting through your templates. {{end}} ``` -An alternative way of writing the "if" and then referencing the same value is -to use "with" instead, which rebinds the pointer `.` within its scope, and -elides the scope if the variable is absent: +An alternative way of writing the "if" and then referencing the same value +is to use "with" instead. With rebinds the context `.` within its scope, +and skips the block if the variable is absent: ``` {{with .Site.Params.TwitterUser}}