Latte: how to use type system?

Type system is main thing for the development of robust applications. Types in PHP have a superiority over other dynamic languages such as Python, Ruby or JavaScript. Nette Framework leads programmers to produce typed and strict code from the beginning. Latte 2.7 brought the type support to templates as well.

To knowing what data or object type each variable is allows

• IDE to correctly autocomplete
• static analysis to detect errors

Two points that significantly improve the quality and convenience of development.

How to declare types?

Three years ago, a tip for hinting in templates in presenter was published on the blog. The idea is to create a class that defines a list of all variables and their types. Using the new features of PHP 7.4, it could look like this:

namespace App\Presenters;

class ArticleTemplate extends Nette\Bridges\ApplicationLatte\Template
{
	public ArticlePresenter $presenter;
	public string $lang;
	public int $page;
	public Model\Page $article;
}

We can now use this class in the template as well. Just add at the beginning:

{templateType App\Presenters\ArticleTemplate}

And we have defined that there will be four variables $presenter, $lang, $page and $article in the template including the corresponding types.

An alternative is to define the types of individual variables directly in the template, ie without creating a class. To do this, use {varType}:

{varType App\Presenters\ArticlePresenter $presenter}
{varType string $lang}
{varType int $page}
{varType Model\Page $article}

Of course, both can be combined. Create a class, as this will ensure completion on the presenter side, link it to the template using {templateType} and use {varType} for other local variables in blocks, etc. This can be understood as an analogy /** @var type $variable */, which is a comment that we sometimes use in PHP code to instruct IDE or static analysis tool.

Also, the type can be specified in {var}, {default} or {define}:

{var Model\Page $page = $items['page']}

{define form, string $name}
	...
{/define}

Note: for historical reasons, it was possible to write variables in the {var} and {default} tags without the leading dollar sign. Because this creates ambiguity whether it is a type or a variable, this syntax is deprecated and Latte will warn you when you use it.

How do you simplify your work?

How to write a template class or {varType} as easy as possible? Get them generated. That is precisely what pair of tags {templatePrint} and {varPrint} do.

If you place one of these tags in a template, the code of class or template is displayed instead of the normal rendering. Then simply select and copy the code into your project.

Nette/application 3.1 (beta) includes an overloaded tag {templatePrint} that generates code that is better suitable for presenters.

The {varPrint} tag lists local variables that are not template parameters. If you want to list all variables, use {varPrint all}.

IDE code completion

The latest version of the PhpStorm Latte plugin can take advantage of the above tags and then suggest based on types. The plugin also knows the types of standard variables such as $user, $presenter, $basePath, etc.

Static analysis

The final goal is that all declared types can also be used for static analysis. For example, to use PHPStan to check templates as easily as other PHP files.

We are working on this and you will see it in one of the next versions of Latte.