diet-ng 1.7.4

Next generation Diet template compiler.

To use this package, run the following command in your project's root directory:

Manual usage
Put the following dependency into your project's dependences section:


Diet is a generic compile-time template system based on an XML-like structure. The syntax is heavily influenced by pug (formerly "Jade") and Haml and outputting dynamic HTML is the primary goal. It supports pluggable transformation modules, as well as output modules, so that many other uses are possible.

See the preliminary Specification for a syntax overview.

This repository contains the designated successor implementation of the module of vibe.d. The current state is almost stable and feature complete and ready for pre-production testing.

DUB link Build Status


doctype html
- auto title = "Hello, <World>";
		title #{title} - example page
		h1= title
		h2 Index
			- foreach (i; 0 .. 3)
				li: a(href="##{i}") Point #{i}
		- foreach (i; 0 .. 3)
			h2(id=i) Point #{i}
				These are the #[em contents] of point #{i}. Multiple
				lines of text are contained in this paragraph.

Generated HTML output:

<!DOCTYPE html>
		<title>Hello, &lt;World&gt; - example page</title>
		<h1>Hello, &lt;World&gt;</h1>
		<ol class="pageindex">
			<li><a href="#0">Point 0</a></li>
			<li><a href="#1">Point 1</a></li>
			<li><a href="#2">Point 2</a></li>
		<h2 id="0">Point 0</h2>
		<p>These are the <em>contents</em> of point 0. Multiple
		lines of text are contained in this paragraph.</p>
		<h2 id="1">Point 1</h2>
		<p>These are the <em>contents</em> of point 1. Multiple
		lines of text are contained in this paragraph.</p>
		<h2 id="2">Point 2</h2>
		<p>These are the <em>contents</em> of point 2. Multiple
		lines of text are contained in this paragraph.</p>

Implementation goals

  • Be as fast as possible. This means moving as many operations from run time to compile time as possible.
  • Avoid any dynamic memory allocations (unless it happens in user code)
  • Let the generated code be fully @safe (unless embedded user code isn't)
  • Be customizable (filters, translation, DOM transformations, output generators), without resorting to global library state
  • Operate on ranges. HTML output is written to an output range, input ranges are supported within string interpolations and filters/translation support is supposed to be implementable using ranges (the latter part is not yet implemented).

Experimental HTML template caching

Since compiling complex Diet templates can slow down the overall compilation process, the library provides an option to cache and re-use results. It is enabled by defining the version constant DietUseCache ( "versions": ["DietUseCache"] in dub.json or versions "DietUseCache" in dub.sdl). It is not recommended to use this feature outside of the usual edit-compile-run development cycle, especially not for release builds.

Once enabled, the template compiler will look for *_cached_#####.d files in the "views/" folder, where the * consists of the full path of the Diet template and ##### represents a unique hash value that identifies the contents of the template, as well as included/extended ones. If found, it will simply use the contents of that file instead of going through the whole compilation process.

At runtime, during initialization, the program will then output the contents of all newly compiled templates to the "views/" folder. For that reason it is currently important that the program is run with the current working directory set to the package directory! A drawback of this method is that outdated cached templates will not be deleted automatically. It is necessary to clear all *_cached_*.d files by hand from time to time.

Note that hopefully this feature will be obsoleted soon by the [work of Stefan Koch on DMD's CTFE engine](

Experimental HTML Live Mode

Building a diet template at compile-time can be slow, as mentioned above. A major drawback of this is that during development, any single change to any diet file requires a complete rebuild of the entire project.

The library now supports a "Live Mode", where any changes to the templates that are strictly HTML related will be rendered on a page refresh, instead of requiring a recompilation. This works by replacing output of the HTML portions of the template with output from a lookup table of strings. Then the strings are rebuilt whenever the file changes. So for example, adding or removing a class from an html element, or fixing herf to href in an anchor element does not require a recompile.

Changes to code portions of the template (i.e. string interpolations such as #{expression} or !{expression}, or any D code escapes such as - foreach(x; range)) will throw an exception, and force you to recompile your project before continuing. This is because the diet engine can deal with changes to string data, but cannot recompile your project for you. And obviously, changing code outside the templates will not change the rendered pages without a recompile. Even adding new lines or inserting lines where HTML did not exist is supported.

For example:

- if(cond)
    - auto a = foobar();

changed to the following will not require a recompile

- if(cond)
    a(href="/") Home
    - auto a = foobar();

The mode is enabled by defining the version constant DietUseLive ( "versions": ["DietUseLive"] in dub.json or versions "DietUseLive" in dub.sdl). It is not recommended to use this in production for the same reasons listed for the caching mode.

To be as efficient as possible, the templates are only parsed on first access, and re-parsed only when a modification in any template or dependent template is detected. Note that it still will not be as efficient as the normal mode which doesn't require any file i/o to render templates.

There are a few limitations to this approach. Like DietUseCache, this REQUIRES the views directory to be accessible to the running executable. In addition, to keep the code generation simple (and avoid a full D parser), certain features do not work with Live Mode. Two such features are type definitions (i.e. structs, unions, or classes), and static functions. There is no escape mechanism to allow these, so you will have to ensure that they are not present in your diet templates, or you will get probably very strange compiler errors.

Any other problems, please report them in github.

This mode and the DietUseCache mode can be combined. Just define both versions in your project's dub configuration.

Examples Directory

The examples directory contains 2 projects showcasing the features of diet.

  • htmlgenerator - Uses diet-ng to generate static html files from diet templates.
  • htmlserver - Simple vibe.d project that shows some features of diet template parsing. Note that there are multiple configurations that show how the caching and live mode work. Please see the file for more details in that directory.
  • Sönke Ludwig
1.7.4 2020-Sep-03
1.7.3 2020-Sep-02
1.7.2 2020-Mar-25
1.7.1 2020-Mar-24
1.7.0 2020-Mar-24
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