PHP Internals News: Episode 66: Namespace Token, and Parsing PHP - Derick Rethans

Planet PHP

PHP Internals News: Episode 66: Namespace Token, and Parsing PHP

London, UK
Thursday, August 6th 2020, 09:28 BST

In this episode of "PHP Internals News" I chat with Nikita Popov (Twitter, GitHub, Website) about his Namespaced Names as a Single Token, and Parsing PHP.

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Derick Rethans 0:16

Hi, I'm Derick, and this is PHP internals news, a weekly podcast dedicated to demystifying the development of the PHP language. This is Episode 66. Today I'm talking with Nikita Popov about an RFC that he's made, called namespace names as token. Hello Nikita, how are you this morning?

Nikita 0:35

I'm fine Derick, how are you?

Derick Rethans 0:38

I'm good as well, it's really warm here two moments and only getting hotter and so.

Nikita 0:44

Same here. Same here.

Derick Rethans 0:46

Yeah, all over Europe, I suppose. Anyway, let's get chatting about the RFC otherwise we end up chatting about the weather for the whole 20 minutes. What is the problem that is RFC is trying to solve?

Nikita 0:58

So this RFC tries to solve two problems. One is the original one, and the other one turned up a bit later. So I'll start with the original one. The problem is that PHP has a fairly large number of different reserved keyword, things like class, like function, like const, and these reserved keywords, cannot be used as identifiers, so you cannot have a class that has the name list. Because list is also a keyword that's used for array destructuring. We have some relaxed rules in some places, which were introduced in PHP 7.0 I think. For example, you can have a method name, that's a reserved keyword, so you can have a method called list. Because we can always disambiguate, this versus the like real list keyword. But there are places where you cannot use keywords and one of those is inside namespace names.

So to give a specific example of code that broke, and that was my, my own code. So, I think with PHP 7.4, we introduced the arrow functions with the fn keyword to work around various parsing issues. And I have a library called Iter, which provides various generator based iteration functions. And this library has a namespace Iterfn. So Iter backslash fn. Because it has this fn keyword as part of the name, this library breaks in PHP 7.4. But the thing is that this is not truly unnecessary breakage. Because if we just write Iter backslash fn, there is no real ambiguity there. The only thing this can be is a namespace name, and similarly if you import this namespace then the way you actually call the functions is using something like fn backslash operator. Now once again you have fn directly before a backslash so there is once again no real ambiguity. Where the actual ambiguity comes from is that we don't treat namespace names as a single unit. Instead, we really do treat them as the separate parts. First one identifier than the backslash, then other identifier, then the backslash, and so on. And this means that our reserved keyword restrictions apply to each individual part. So the whole thing.

The original idea behind this proposal was actually to go quite a bit further. The proposal is that instead of treating all of these segments of the name separately, we treat it as a single unit, as a single token. And that also means that it's okay to use reserved keywords inside it. As long as like the whole name, taken together is not a reserved keyword. The idea of the RFC was to, like, reduce the impact of additional reserved keywords, introduc

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