Temple

Surprisingly Flexible, Compile Time, Zero Overhead, Embedded Template Engine for D

About

Temple is a templating engine written in D, allowing D code to be embedded and executed in text files. The engine converts text to code at compile time, so there is zero overhead interpreting templates at runtime, allowing for very fast rendering.

Temple supports passing any number of arbitrary variables to templates, as well as nesting and yielding templates within each other, capturing blocks of template code, and optional fine-grain filtering of generated text (e.g for escaping generated strings/safe strings).

Vibe.d compatible! See the Vibe.d Usage section.

Temple works with

• DMD >= 2.066
• LDC >= 0.15-alpha1
• GDC >= 4.9.2

And probably more, but that's what it's been officially tested with.

Table of Contents

• Usage
• The Temple Syntax
• Contexts
• Compiling Templates
• Templates from Files
• Nested Templates
• Layouts and Yielding
• Capture Blocks
• Helpers
• Filters
• TempleFilter
• Vibe.d Usage
• Example: Simple Webpages

Usage

If using dub, include temple as a dependency in dub.json, or all of the files in src/temple in your build process, and import temple;.

Going from a template string to a rendered template follows the process:

• Compile the template with the compile_temple or compile_temple_file functions, resulting in a CompiledTemple
• Call 'toString' or 'render' on the resulting CompiledTemple
• Optionally pass in a TempleContext to pass variables to the template

Optional Filters can be supplied to compile_template[_file] to filter dynamic template content.

The Temple Syntax

The template syntax is based off of that of eRuby (but can be changed by modifying temple/delims.d). D statements go between <% %> delimers. If you wish to capture the result of a D expression, place it between <%= %> delimers, and it will be converted to a string using std.conv's to.

Shorthand delimers are also supported: A line beginning with % is considered a statement and executed; a line beginning with %= is evaluated and the result is written to the output stream.

Note that expressions within <%= %> and %= should not end with a semicolon, while statements within <% %> and % should.

Quick Reference:

Input	Output
foo	foo
<% "foo"; %>	<no output>
<%= "foo" %>	foo
%= "foo" ~ " " ~ "bar"	foo bar
% "foo";	<no output>

Foreach

% foreach(i; 0..3) {
	Index: <%= i %>
% }

Index: 0
Index: 1
Index: 2

Foreach, alt

% import std.conv;
<% foreach(i; 0..3) { %>
	%= "Index: " ~ to!string(i)
<% } %>

Index: 0
Index: 1
Index: 2

If/else if/else statements

% auto a = "bar";
% if(a == "foo") {
	Foo!
% } else if(a == "bar") {
	Bar!
% } else {
	Baz!
% }

Bar!

Overall usage

auto hello = compile_temple!`Hello, <%= var.name %>!`
auto ctx = new TempleContext();
ctx.name = "Jimmy";

writeln(hello.toString(ctx));

Hello, Jimmy!

Contexts

The TempleContext type is used to pass variables to templates. The struct responds to opDispatch, and returns variables in the Variant type. Use Variant#get to convert the variable to its intended type. TemplateContext#var(string) is used to retrieve variables in the context, and can be called directly with var in the template:

auto context = new TempleContext();
context.name = "dymk";
context.should_bort = true;

Passed to:

<% /* Variant can be converted to a string automatically */ %>
Hello, <%= var("name") %>

<% /* Conversion of a Variant to a bool */ %>
% if(var("should_bort").get!bool) {
	Yep, gonna bort
% } else {
	Nope, not gonna bort
% }

<% /* Variants are returned by reference, and can be (re)assigned */ %>
<% var("written_in") = "D" %>
Temple is written in: <%= var("written_in") %>
}

Results in:

Hello, dymk
Yep, gonna bort
Temple is written in: D

Variables can also be accessed directly via the dot operator, much like setting them.

auto context = new TempleContext();
context.foo = "Foo!";
context.bar = 10;

<%= var.foo %>
<%= var.bar %>

<% var.baz = true; %>
<%= var.baz %>
}

Prints:

Foo!
10
true

For more information, see the Variant documentation on the dlang website

Using CompiledTemple

Both compile_temple!"template string" and compile_temple_file!"filename" return a CompiledTemple. The CompiledTemple exposes two rendering methods, toString, and render, both of which take an optional TemplateContext.

string CompiledTemple#toString(TempleContext = null)

---

Evaluates the template and returns the resulting string

import
  temple.temple,
  std.stdio,
  std.string;

void main()
{
	auto tlate = compile_temple!"foo, bar, baz";
	writeln(tlate.toString()); // Prints "foo, bar, baz"
}

An example passing a TempleContext:

void main()
{
	auto tlate = compile_temple!q{
		Hello, <%= var("name") %>
	};

	auto context = new TempleContext();
	context.name = "dymk";

	writeln(tlate.toString(ctx)); // Prints "Hello, dymk"
}

void CompiledTemple#render(Sink, TempleContext = null)

---

Incrementally evaluates the template into Sink, which can be one of the following:

• an std.stdio.File
• an arbitrary OutputRange (as determined by std.range.isOutputRange!(T, string))
• a function or delegate that can take a string: void delegate(string str) {}

Using render greatly decreases the number of allocations that must be made compared to toString.

auto tlate = compile_temple!q{
	Hello, <%= var("name") %>
};

tlate.render(stdout); // render into stdout

// incrementally render into function/delegate
tlate.render(function(str) {
	write(str);
});

compile_temple_file

compile_temple_file is the same as compile_temple, but takes a file name to read as a template instead of the template string directly. Temple template files typically end with the extension .emd ("embedded d").

template.emd:

It's <%= var("hour") %> o'clock.

main.d:

import
  templ.templ,
  std.stdio;

void main() {
	auto tplate = compile_temple_file!"template.emd";

	auto context = new TempleContext();
	context.hour = 5;

	tplate.render(stdout);
}

It's 5 o'clock

Nested Templates

#render can be called within templates to nest templates. By default, the current context is passed to the nested template, and any filters applied to the nester are applied to the nestee. A different context can be passed explicitly by calling #render_with(TemplateContext) instead.

a.emd

<html>
	<body>
		<p>Hello, from the 'a' template!</p>
		<%= render!"b.emd"() %>
	<body>
</html>

b.emd

<p>And this is the 'b' template!</p>

Rendering a.emd would result in:

<html>
	<body>
		<p>Hello, from the 'a' template!</p>
		<p>And this is the 'b' template!</p>
	<body>
</html>

Layouts and Yielding

Templates can be made into parent layouts, where the child is rendered when #yield is called. Setting the child for a template is done by calling layout on the parent.

void main()
{
	auto parent = compile_temple!"before <%= yield %> after";
	auto child  = compile_temple!"between";

	auto composed = parent.layout(&child);
	composed.render(stdout);
}

before between after

Capture Blocks

Blocks of template can be captured into a variable, by wrapping the desired code inside of a delegate, and passing that to capture. Capture blocks can be nested. Capture blocks do not render directly to a string, but rather a range, meaning that evaluating a capture block will result in evaluating the entire capture block multiple times.

Capture has the signature string capture(T...)(void delegate(T) block, T args), and can be called from user defined functions as well (See the Helpers section).

Example:

<% auto outer = capture(() { %>
	Outer, first
	<% auto inner = capture(() { %>
		Inner, first
	<% }); %>
	Outer, second

	<%= inner %>
<% }); %>

<%= outer %>

Outer, first
Outer, second
	Inner, first

Helpers (A-la Rails View Helpers)

Helpers aren't a built in feature of Temple, but they are a very useful pattern for DRYing up templates. Here's a partial implementation of Rails' form_for helper:

<%
import std.string;
struct FormHelper
{
	string model_name;

	auto field_for(string field_name, string type="text")
	{
		if(model_name != "")
		{
			field_name = "%s[%s]".format(model_name, field_name);
		}

		return `<input type="%s" name="%s" />`.format(type, field_name);
	}

	auto submit(string value = "Submit")
	{
		return `<input type="button" value="%s" />`.format(value);
	}
}

auto form_for(
	string action,
	string name,
	void delegate(FormHelper) block)
{
	auto form_body = capture(block, FormHelper(name));
	return `
		<form action="%s" method="POST">
			%s
		</form>`.format(action, form_body);
}
%>

<%= form_for("/shorten", "", (f) { %>
	Shorten a URL:
	<%= f.field_for("url") %>
	<%= f.submit("Shorten URL") %>
<% }); %>

<%= form_for("/person", "person", (f) { %>
	Name: <%= f.field_for("name") %>
	Age: <%= f.field_for("age") %>
	DOB: <%= f.field_for("date_of_birth", "date") %>
	<%= f.submit %>
<% }); %>

Renders:

<form action="/shorten" method="POST">
	Shorten a URL:
	<input type="text" name="url" />
	<input type="button" value="Shorten URL" />
</form>

<form action="/person" method="POST">
	Name: <input type="text" name="person[name]" />
	Age: <input type="text" name="person[age]" />
	DOB: <input type="date" name="person[date_of_birth]" />
	<input type="button" value="Submit" />
</form>

Filters

Filters are a way to filter and transform the dynamic parts of the template, before it is written to the output buffer. A filter takes the form of a struct or class that defines various overloads of the static method temple_filter. The temple_filter methods can either:

• Take two parameters: a TempleOutputStream to write their result to, and the input to filter, e.g.
  • `void temple_filter(ref TempleOutputStream ob, string str) { ob.put(str); }
• Take one parameter and return a string:

Example, wrapping evaluated text in quotes:

struct QuoteFilter
{
	static string temple_filter(string raw)
	{
		return `"` ~ raw ~ `"`;
	}

	static string temple_filter(T)(T raw)
	{
		return temple_filter(to!string(raw));
	}
}

auto render = compile_temple!(QuoteFilter, q{
	Won't be quoted
	<%= "Will be quoted" %>
	<%= 10 %>
});
writeln(templeToString(&render));

Won't be quoted
"Will be quoted"
"10"

The temple_filter method isn't limited to filtering only strings, however. Any arbitrary type can be passed in. They can also define any arbitrary methods to use in the template, provided they don't clash with the methods that TempleContext defines.

Example, implementing safe/unsafe strings for conditional escaping of input:

private struct SafeDemoFilter
{
	static private struct SafeString
	{
		string value;
	}

	static string temple_filter(SafeString ts)
	{
		return ts.value;
	}

	static string temple_filter(string str)
	{
		return "!" ~ str ~ "!";
	}

	static SafeString safe(string str)
	{
		return SafeString(str);
	}
}

auto templ = compile_temple!(q{
	foo (filtered):   <%= "mark me" %>
	foo (unfiltered): <%= safe("don't mark me") %>
}, SafeDemoFilter);

templ.render(stdout);

foo (filtered):   !mark me!
foo (unfiltered): don't mark me

Filters are propagated to nested templates:

a.emd:

<%= safe("foo1") %>
<%= "foo2" %>
foo3
<%= render!"b.emd" %>
foo4

b.emd

<%= safe("bar1") %>
<%= "bar2" %>
bar3

a.emd rendered with the SafeDemoFilter:

foo1
!foo2!
foo3
bar1
!bar2!
bar3
foo4

TempleFilter

TempleFilter is not a filter itself, but rather allows a filter to be applied to entire family of Temple templates, grouping them under a single name.

Example usage:

struct MyFilter {
	static string temple_filter(string unfiltered) {
		return "!" ~ unfiltered ~ "!";
	}
}

// All Temple templates under Filtered will have MyFilter applied to them
alias Filtered = TempleFilter!MyFilter;

auto child = Filtered.Temple!`
	foo
	<%= "bar" %>
`;

auto parent = Filtered.TempleLayout!`
	header
	<%= yield %>
	footer
`

parent.layout(&child).render(stdout);

Which would render:

header
foo
!bar!
footer

Vibe.d Integration

Temple will expose functions for integrating with Vibe.d if compiled together (e.g. Have_vibe_d is defined) The addition to the Temple API is:

• void renderTemple(string temple)(HTTPServerRequest, Context = null)
• void renderTempleFile(string filename)(HTTPServerRequest, Context = null)
• void renderTempleLayoutFile(string layoutfile, string partialfile)(HTTPServerRequest, Context = null)
• struct TempleHtmlFilter

where Context can be an HTTPServerResponse, or a TempleContext. If it is a HTTPServerResponse, then the contents of the params hash will be the context for the template.

Usage is similar to Vibe.d's render function:

void doRequest(HTTPServerRequest req, HTTPServerResponse res) {

	// Client requested with query string `?name=foo`

	req.renderTemple!(`
		Hello, world!
		And hello, <%= var.name %>!
	`)(res);

}

Would result in this HTTP response:

Hello, world!
And hello, foo!

---

Dynamic content is passed through Vibe's HTML filter before being rendered, unless it is marked as safe, by calling safe("your string").

void doRequest(HTTPServerRequest req, HTTPServerResponse res) {

	// Client requested with query string `?name=foo`

	req.renderTemple!(`
		<html>
			<body>
				Here's a thing!
				<%= "<p>Escape me!</p>" %>
				<%= safe("<span>Don't escape me!</span>") %>
			</body>
		</html>
		Hello, world!
		And hello, <%= var.name %>!
	`)(res);

}

Would result in the HTTP response:

<html>
	<body>
		Here's a thing!
		&lt;p&gt;Escape me!&lt;/p&gt;
		<span>Don't escape me!</span>
	</body>
</html>

Example: Simple Webpages

Here's a slightly more complex example, demonstrating how to use the library to render HTML templates inside of a common layout.

void main()
{
	auto parent = compile_temple_file!"layout.html.emd";
	auto child  = compile_temple_file!"_partial.html.emd";

	parent.layout(&child).render(stdout);
}

layout.html.emd

<html>
	<head>
		<title>dymk's awesome website</title>
	</head>
	<body>
		%= render!"common/_sidebar.html.emd"()
		%= yield
		%= render!"common/_footer.html.emd"()
	</body>
</html>

common/_sidebar.html.emd

<ul>
	<li><a href="/">Home</a></li>
	<li><a href="/about">About</a></li>
	<li><a href="/contact">Contact</a></li>
</ul>

common/_footer.html.emd

<footer>
	2013 (C) dymk .: built with Temple :.
</footer>

_partial.html.emd

<section>
	TODO: Write a website
</section>

Output:

<html>
	<head>
		<title>dymk's awesome website</title>
	</head>
	<body>
		<ul>
			<li><a href="/">Home</a></li>
			<li><a href="/about">About</a></li>
			<li><a href="/contact">Contact</a></li>
		</ul>
		<section>
			TODO: Write a website
		</section>
		<footer>
			2013 (C) dymk .: built with Temple :.
		</footer>
	</body>
</html>

Notes

The D compiler must be told which directories are okay to import text from. Use the -J<folder> compiler switch or stringImportPaths in Dub to include your template directory so Temple can access them.

For more examples, take a look atsrc/temple/test/common.d's unittests; they provide very good coverage of the library's abilities.

License

Temple is distributed under the Boost Software License.