I'm kinda against having a fluent interface as it doesn't really make sense to have a fluent here (it's not a builder...)

Adding a mutable state why not, and maybe keep it immutable (returning a new instance with the property set correctly) would be even better IMO.

(Hence my 😕 / 👎 reaction)

@Taluu Maybe fluent interface is not correct term here, I meant a bunch of setters by it just to mutate the state (that's exactly what's been done.).

Sorry for my bad english but what's the difference between this PR and Adding a mutable state why not?

You made it fluent (returning $this) is the key difference here. :)

Oh, I got you :-) I don't mind changing the PR so setters would become something like:

public function setName(string $name): self
{
    // ...validating $name...
    $clone = clone $this;
    $clone->name = $name;

    return $clone;
}

But I personally prefer $this :-)
Anyway, let's wait on other opinions.

Even better : make withers (withName...).

Or remove the return and make it mutable.

@Taluu

I updated the PR with withers keeping the Cookie immutable. Appreciate it if you take a look.

I need this ! but sad to have to wait for 5.2.0 release to get mutable cookie :/

Thanks for your explanations @ns3777k, I missed that some attributes should remain nullable.
I pushed a third commit on your fork with additional changes.
As a last step, I think we should group all wither methods at the beginning of the class, before the getters.

Thanks for clarification! @nicolas-grekas I'm gonna move the withers up.

Thank you @ns3777k.