On 5/25/16 9:03 AM, Nikita Popov wrote:
On Wed, May 25, 2016 at 10:30 AM, Joe Watkins <pthre...@pthreads.org> wrote:
Morning Dmitry,
> I made this check(s) to be invariant. You may like to do this
differently...
I think this is what everyone expects, isn't it ?
I did omit to mention that part ...
> RFC doesn't define how uninitialized nullable typed properties should
behave.
It does:
> *Nullable typed properties will not raise an exception when accessed
before initialization.*
I don't agree with this choice, for three reasons:
a) This unnecessarily restricts what can be expressed in the type system.
With these semantics it will no longer be possible to express that a
property should be nullable, but have no default value. This situation is
not uncommon in practice, in particular anytime you have a nullable
constructor argument, you will want the corresponding property to be
nullable without a default, to ensure that it is explicitly initialized.
b) This directly contradicts the meaning of ?Type for parameters. For
parameters ?Type means that it's a nullable parameter **without a default
value**. That's the very thing that distinguishes it from the Type $prop =
null syntax. And now ?Type for properties should mean the exact opposite?
c) If you view this in a larger scope of union types, this *special case*
becomes even more weird. Why does the particular union Type|null get
special treatment, while all other unions don't? Or is it actually not
specific to "null", but to single value types? E.g. if we also allowed
Type|false, would that also receive an implicit false default value? What
about the type null|false? Does that get an implicit default, and if so,
which? I realize this is not quite in scope for type properties, but the
further evolution of the type system should be kept in mind.
Please keep things consistent: If there is not default, there is no default.
Object properties being in a uninitialized state is unfamiliar in
current PHP practice. We are accustomed to not worrying about an
"uninitialized error" when we read a property. We are assured to get
either null or whatever was last written to the property.
I suspect this unfamiliarity lies behind some people's preference for an
implicit initial null value of a nullable typed property.
But I'm inclined to agree with Nikita that the following should be
different:
public ?Client $mark;
public ?Client $mark = null;
... and that the difference should be coherent with that between:
function con(?Client $mark) {}
function con(?Client $mark = null) {}
... which is that you *must* give $mark value in the first and you don't
need to in the second because it has an explicit default. We are
more-or-less accustomed already to the difference between:
function con(Client $mark) {}
function con(Client $mark = null) {}
... so I think your consistency argument is good.
Moreover, the "good old" implicit initial null for untyped properties
(i.e. that `public $foo;` means `public $foo = null;`) is just a lazy
shortcut that I wouldn't defend except for BC, which isn't an issue here.
Tom
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