By the way, I can see somewhat where @Werner and @conradfr are coming from though, having used (and still using) template-inheritance based templates in several applications.
Personally I feel that there is some additional (superficially seemingly unneeded) complexity within the phoenix view implementation due to the concepts of layouts (root and app layout). With jinja2-style templates, there is just one template entry point/file. It is only within that template file that we usually determine which “layout” we use, and the structure of the whole HTML document is determined only based on that template.
Having to do a put_layout or setting the root layout somewhere in the plug pipeline feels a bit out of place when you are just concerned with rendering a the HTML document based on a template.
Suddenly there are three things that determine the document structure as a whole, and those are not really that co-located with the rest of the view/template/component stuff. It somehow feels a bit like mixing and spreading concerns. The router is for routing, the controller for calling your logic and returning html/json or whatever, and the view for the intricacies of building up the structure of an HTML document.
Luckily we now have components with slots as @josevalim mentioned though, and coming to think of it, is the root/app layout thing really still needed? I mean, couldn’t a layout just be wholly defined in a <.base_layout /> component (including the html, head and body wrapping things needed for e.g. liveview)?
Then, all the things about the html output could be determined through that component (e.g. slots for additional js/css things based on the template) and it’s children.
Additionally, the view implementation could be cleaned up a bit because put_layout/2, plug :put_root_layout, html: {MyWeb.Layouts, :root} and friends are not needed anymore.
Or would this be too far fetched or maybe even blatantly wrong thing to aspire @josevalim (or @chrismccord)?