On 02/02/2023 14:19, someniatko wrote:
I suggest to introduce an official type-checker / static analyser / preprocessor / transpiler for PHP, somewhat similar to TypeScript in the JavaScript world, which will allow to introduce the features otherwise impossible for the PHP world, at the cost of including an additional transpilation step.
This is something I have thought about a lot over the years, and in some ways, it is very appealing; but it does have some problems.
One of the biggest is the concept of "type erasure": in a pre-processed or transpiled language, features like Reflection are crippled by not knowing the full information present in the source code. More importantly, dynamic language features - of which PHP has many - also have no access to the type information. That means that a List<Dog> can sometimes end up with a Cat in it at run-time, because a dynamic call doesn't know that's a problem.
I think it's interesting to look around at different approaches to this elsewhere:
You mention Python, which I think has probably the *worst* approach: it has official syntax which appears to convey type information, but doesn't actually provide any guarantees if you forget to run an external tool. Outside of that tool, the type information is just another type of comment, just less clearly so than the annotations understood by tools like PhpStan and Psalm in today's PHP.
Another approach is TypeScript, which is essentially a complete language in its own right, with JavaScript as a compilation target. As I understand it, you can call JS code from inside a TS project (and vice versa, once the TS is transpiled), but that won't always be seamless, so the two languages will tend to end up with separate ecosystems of libraries and tooling. Implementing a new language also takes time, and ultimately money - in this case, Microsoft's money.
A similar project, closer to PHP's heart, is Hack; the main difference being that rather than transpiling to PHP, it initially aimed to compile both languages to a common bytecode, to be executed in a shared VM. However, it turns out that as well as *adding* features on top of PHP, it was necessary for Hack to *remove* features of PHP that weren't compatible with a static typing system, and eventually the interoperability was dropped altogether. It also has money behind it, in this case from Facebook.
Dart, which was written completely from scratch (the money this time is Google's), has a type system checked *mostly* at compile-time, but with certain run-time assertions inserted where the compiler can't prove soundness. The approach seems appealing, but PHP would probably end up with a lot of such cases - all the features that the Hack team decided to remove - leading to poor performance and confusing developer experience.
I don't have a conclusion to this e-mail, I just thought I'd throw out these thoughts.
Regards, -- Rowan Tommins [IMSoP] -- PHP Internals - PHP Runtime Development Mailing List To unsubscribe, visit: https://www.php.net/unsub.php
