Mallmotorer

Mallmotorer, or template engines, are software components used to generate text output by merging a template with a data model. The template contains placeholders and rules that determine how data should be presented. At render time the engine replaces placeholders with actual values and evaluates constructs such as loops and conditionals to produce a final document, page, or email.

They can operate on the server to produce web pages or documents, or on the client to render dynamic content in interactive applications. Templates often aim to separate content from presentation, allowing designers and developers to work independently and enabling easier maintenance and reuse.

Two broad approaches exist. Logic-less engines limit what can be expressed in templates to data substitution and simple sections, encouraging a strict separation between data and markup. More expressive engines provide broader control structures, functions, and filters, offering greater flexibility at the cost of tighter coupling between logic and presentation. Common features across mallmotorer include variables, sections or loops, conditionals, partials or includes, and escaping to prevent security issues such as script injection. Caching and extensibility are also important for performance and customization.

Popular examples include Mustache (logic-less), Twig, Jinja2, Liquid, ERB, and FreeMarker. They are used in web frameworks as well as in document generation and email templating. When choosing a mallmotor, considerations include language compatibility, template syntax, performance, security features, and the desired balance between simplicity and expressiveness.