Hey folks.
Am 26.08.24 um 11:26 schrieb Bilge:
On 26/08/2024 10:03, Andreas Leathley wrote:
On 24.08.24 18:49, Bilge wrote:
For me there is another question. When using interfaces and classes,
default values can be introduced, like this:
interface CompressionInterface
{
public function compress(string $data, int $level): string;
}
class GzipCompression implements CompressionInterface
{
public function compress(string $data, int $level = 4): string
{
// do something
}
}
When I have the GzipCompression class, I would know there is a default
value for $level, but when using the interface there might or might not
be a default value, depending on the implementation. As far as I read
the RFC, using "default" when there is no default would lead to a
runtime exception, but there is no way of finding out if there is a
default if you do not already know. Being able to test that could be
useful, although I am not sure about the syntax for that. In the example
when getting CompressionInterface, I might test for the existence of a
default value of $level and leave it at the default if there is a
default (maybe I know that some implementations have a default value,
others don't). One could test the specific implementation with
instanceof checks, but the advantage of "default" could be that you do
not need to know the implementation and could only adapt to possibly
defined default values.
Hi Andreas,
Thanks for this question; I find this super interesting because it's
something we haven't thought about yet. I must admit I completely
overlooked that, whilst an interface /can/ require implementers to
specify a default, in the case that they do not, it is still valid for
implementations to selectively elect to provide one. Therefore I can
append to your example the following case (I removed the `string` return
type for now):
class ZipCompression implements CompressionInterface
{
public function compress(string $data, int $level)
{
var_dump($level);
}
}
new GzipCompression()->compress('', default ?? 6);
new ZipCompression()->compress('', default ?? 6);
In this case, we get the following output:
int(4)
Fatal error: Uncaught ValueError: Cannot pass default to required
parameter 2 of ZipCompression::compress()
I would like to fix this if possible, because I think this should be
valid, with emphasis on /if possible/, because it may be prohibitively
complex. Will update later.
Cheers,
Bilge
I think I am missing something here. From my understanding we are
*either* coding against the interface and then it should not be possible
to use `default` at all as no default is set in the interface. So the
fatal error is totally valid for me.
*Or* we are coding against the actual implementations. Then it is
totally valid IMO that providing `default` when no default is set in the
concrete implementation of the function signature raises a fatal error.
So in the example above it's either
new GzipCompression()->compress('', default ?? 6);
new ZipCompression()->compress('', default ?? 6);
and it is absolutely valid that the second one triggers a fatal error as
no default is set in the concrete implementation.
Or it's something like
/** @var CompressionInterface $compression */
foreach ([new GzipCompression, new ZipCompression] as $compression) {
$compression->compress('', default ?? 6)
}
in which case it should definitely fail as the interface doesn't provide
a default.
Cheers
Andreas
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