Le 01/07/2021 à 17:25, Larry Garfield a écrit :
The most famous use case right now for with-er objects is PSR-7, which is where
the naming convention comes from. I cannot say how widely used it is outside
of FIG-inspired value objects, but I am pretty sure it is used.
As long as you implement the with-ers manually, you don't need "clone
with", you can create a new instance the old way (i.e. using the object
constructor). Once there will be a "clone with" like feature, PSR's will
be able to evolve, but right now they'll work as they are, and it's fine.
The key point is that you rarely need to clone service objects; value objects,
however, you have to clone if you want to mutate. Look at any PSR-7 pipleline.
By design, it calls $request->withBlah($newBlah) a lot, and returns a new
object. That's the model that we want to support, and make *easier* to do, but
the readonly flag makes *harder* to do than the status quo today. (See my
previous post on the subject in the last thread.)
That's the whole point of readonly properties, not to mutate. If you
want readonly mutable properties, don't write the readonly keyword. Any
attempt in mutating something that was explicitly closed sounds like
you're doing something really wrong.
I mean by that that not all objects are services, value objects are
values, they're not meant to mutate. If you need a different value, you
use the object constructor. The right way in my opinion for PSR-7
pipeline is to stick with the with-ers, because it makes it explicit, by
contract, of what you are attempting to achieve in your middlewares, and
yet still work using an interface and not an instance: this model is
very flexible and highly extensible. And yes PSR-7 doesn't fit with
readonly properties, but that's not a problem, having readonly
properties doesn't mean you actually have to use them everywhere.
There are use cases for readonly that don't require cloning. For those, it's
useful. I personally think asymmetric visibility would render readonly
unnecessary and redundant, but Nikita disagrees, and he's the one writing the
code so... :-)
Yeah, I very much like asymmetric visibility as well. But readonly and
asymmetric visibility are not incompatible. They both answer to
different needs, some of those use cases probably intersect, but
readonly properties have the nice advantage of allowing you to write
pure immutable objects with a very simple syntax, and I love that,
there's much code I wrote and do maintain that'll fit perfectly with that.
Regards,
--
Pierre
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