Re: [RFC] [Discussion] Never parameters

On Mon, Mar 10, 2025 at 12:05 PM Daniel Scherzer < daniel.e.scherzer@gmail.com> wrote: > Hi internals, > > I'd like to start discussion on a new RFC about allowing > never for > parameter types when declaring a method. > > * RFC: https://wiki.php.net/rfc/never-parameters-v2 > * Implementation: https://github.com/php/php-src/pull/18016 > > -Daniel > Since a lot of the discussion seems to be around static analysis and whether there is a real use case for this, I wanted to share another use case I just came across: in the thephpleague/commonmark package, different renderers are added to render different types (subclasses) of League\CommonMark\Node\Node. You can see the interface for renderers at [1]. The overall interface supports being called with any Node type, but each underlying renderer expects to be called with a *narrower* type than that. To avoid LSP violations, the renderers * have a Node typehint * have a documentation comment with the actual subclass of Node that they support * manually throw an exception on invalid values See, e.g., the default renderer for paragraphs[2]. This seems like exactly the place where you would find it useful to have never parameters. The current implementation * uses comments and static analysis tools to document the restriction * manually throws an exception when violated Whereas if the base class had a never parameter, it could * use language typehints to document the restriction * have the exception enforced automatically I don't think we should be worried about the fact that, under static analysis, we don't know what type of value is accepted for a never parameter, because under actual operation, you can always just manually throw an exception for a type you don't want, like commonmark does. -Daniel [1] https://github.com/thephpleague/commonmark/blob/2.6/src/Renderer/NodeRendererInterface.php [2] https://github.com/thephpleague/commonmark/blob/2.6/src/Renderer/Block/ParagraphRenderer.php