Re: [Proposal] Struct Data Types

On Fri, Mar 15, 2019 at 4:26 PM Nikita Popov <nikita.ppv@gmail.com> wrote: > On Fri, Mar 15, 2019 at 4:16 PM Levi Morrison <levim@php.net> wrote: > >> Personally, I think pass by-value with copy-on-write semantics like >> arrays is the sweet spot. Mutability is fine if it is localized. >> > > If we introduce something like this, I think it is very important that it > does not use the same property access syntax as ordinary objects, which are > not copy-on-write. I do not want to be second guessing whether $x->y = $z > is going to copy or not. Possibly such struct types should indeed use the > array access syntax, because array access is generally copy-on-write (the > exception being ArrayAccess objects). > > >> I think having a no-constructor construction syntax is also a good >> idea. I've discussed it with a few people, but don't can't remember if >> it's ever been brought up on-list. Basically, the idea is to use a >> JSON-like syntax with the type-name in front, and I think it can be >> fine to use on regular classes that don't have a constructor too: >> >> struct Point2d { >> float $x; >> float $y; >> } >> >> $origin = Point2D { x: 0, y: 0 }; >> >> This syntax has no conflicts. We could also add an object literal >> syntax for creating ad-hoc stdClass objects like so: `$obj = { x: 1, >> y: 1}`. This has an ambiguity, but I believe I have solved the issue >> without too much trouble once before. >> > > This syntax has no conflicts in the sense that the grammar is unambiguous, > but I believe it does conflict under LR(1). The problem is the alternative > array access syntax, which makes Point2D { x } currently valid syntax. We > can distinguish it at the ":", but by this point a shift/reduce descision > on "{" must have already been made. (We can likely hack around this.) > Taking back this one: Turns out that we currently don't support the CONSTANT{$x} syntax -- it's an oversight from the uniform variable syntax RFC, which generally established syntax parity for the [] and {} array access syntax, but missed support for this particular case. In this case it happens to be in our favor :) Nikita