Class Re-implementation Mechanism

Hi again, internals

My marathon of some crazy ideas continues :D, with less crazy one this
time.

Idea

Allow "reimplementing" the non-static public API (that is public
properties and methods, excluding constructor) of a class by other
classes like this:

final class interface A {
    public string $s;

    public function __construct(string $s) { $this->s = $s; }

    public static function fromInt(int $i): self { return new
self((string) $i); }

    public function foo(): int { return 42; }
}

final class B implements A {
    public string $s = 'hello';

    public function foo(): int { return 69; }
}

function usesA(A $param): void {}

usesA(new B); // this works

Explanation

Consider there is a class like this:

final class Service {
    public function __construct(private SomeDependency $dependency) {}
    // ...
}

final class SomeDependency {
    // ...
}

We want to write some tests for the Service class, but we don't want
to use a real SomeDependency instance
during tests. A common approach is to either extract an interface
(JUST to make it testable), or to drop the
final keyword and allow extending the class.

Both approaches have their flaws:

• extracting an interface unnecessarily complicates the system, where
  only one "real" implementation of an interface is assumed.
• dropping the final keyword allows for the rabbit-hole of
  inheritance abuse, like greatly described in this article:
  https://front-line-php.com/object-oriented

I believe I came up with a better idea: what if we could leave both
benefits of prohibiting the inheritance abuse and also allow not to
clutter our namespace with excess entities like interfaces? I hereby
suggest to combine the responsibilities of a class and an interface
into one thing like that:

final class interface C {}
final class D implements C {}

Now other classes can "implement" this class as well. Introduction of
the new syntax (class interface) also solves BC problem - if you
want to forbid your classes to be reimplemented whatsoever, you can
still stick to the final class syntax. Although it is also possible
to allow "reimplementing" ANY class, then new syntax is not needed -
but some library writers like Marco Pivetta could be sad about that I
suppose.

Soo..., what do you think? Could this be a valuable addition to the
language?

Regards,
Illia / someniatko

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Although I undeterstand and agree with the annoyance of both limitations
presented, I think one important factor that makes this an issue lies with
PSR-4 and autoloading. If you could declare the interface and the
implementation in the same file, as you do with Typescript, the drawback of
extracting an interface for testing would be greatly diminished.
Unfortunately undoing PSR-4 shortcomings and getting something baked into
Composer or PHP to address this seems fairly challenging.

Hi again, internals

My marathon of some crazy ideas continues :D, with less crazy one this time.

Idea

Allow "reimplementing" the non-static public API (that is public
properties and methods, excluding constructor) of a class by other
classes like this:

final class interface A {
    public string $s;

    public function __construct(string $s) { $this->s = $s; }

    public static function fromInt(int $i): self { return new
self((string) $i); }

    public function foo(): int { return 42; }
}

final class B implements A {
    public string $s = 'hello';

    public function foo(): int { return 69; }
}

function usesA(A $param): void {}

usesA(new B); // this works

Explanation

Consider there is a class like this:

final class Service {
    public function __construct(private SomeDependency $dependency) {}
    // ...
}

final class SomeDependency {
    // ...
}

We want to write some tests for the Service class, but we don't want
to use a real SomeDependency instance
during tests. A common approach is to either extract an interface
(JUST to make it testable), or to drop the
final keyword and allow extending the class.

Both approaches have their flaws:

• extracting an interface unnecessarily complicates the system, where
  only one "real" implementation of an interface is assumed.
• dropping the final keyword allows for the rabbit-hole of
  inheritance abuse, like greatly described in this article:
  https://front-line-php.com/object-oriented

I believe I came up with a better idea: what if we could leave both
benefits of prohibiting the inheritance abuse and also allow not to
clutter our namespace with excess entities like interfaces? I hereby
suggest to combine the responsibilities of a class and an interface
into one thing like that:

final class interface C {}
final class D implements C {}

Now other classes can "implement" this class as well. Introduction of
the new syntax (class interface) also solves BC problem - if you
want to forbid your classes to be reimplemented whatsoever, you can
still stick to the final class syntax. Although it is also possible
to allow "reimplementing" ANY class, then new syntax is not needed -
but some library writers like Marco Pivetta could be sad about that I
suppose.

Soo..., what do you think? Could this be a valuable addition to the language?

Regards,
Illia / someniatko

--

To unsubscribe, visit: https://www.php.net/unsub.php

This reminds me a lot of C#'s "extension methods" which are quite
useful. If PHP had something like that, you could do some really nice
things:

class BMock {
public static function bar from A(): int { return 69; }
}

$a = new A(123);
echo $a->bar(); // output: 69

class BReal {
public static function bar from A(): int { return $self->foo(); }
}

// error A::bar() already defined on BMock

where from A is syntax sugar for public function bar(A $self) {}
and trying $a->bar() is simply syntax sugar for BMock::bar($a);

Hi Someniatko,

Hi again, internals

My marathon of some crazy ideas continues :D, with less crazy one this
time.

Idea

Allow "reimplementing" the non-static public API (that is public
properties and methods, excluding constructor) of a class by other
classes like this:

final class interface A {
    public string $s;

    public function __construct(string $s) { $this->s = $s; }

    public static function fromInt(int $i): self { return new
self((string) $i); }

    public function foo(): int { return 42; }
}

final class B implements A {
    public string $s = 'hello';

    public function foo(): int { return 69; }
}

function usesA(A $param): void {}

usesA(new B); // this works

Explanation

Consider there is a class like this:

final class Service {
    public function __construct(private SomeDependency $dependency) {}
    // ...
}

final class SomeDependency {
    // ...
}

We want to write some tests for the Service class, but we don't want
to use a real SomeDependency instance
during tests. A common approach is to either extract an interface
(JUST to make it testable), or to drop the
final keyword and allow extending the class.

Both approaches have their flaws:

• extracting an interface unnecessarily complicates the system, where
  only one "real" implementation of an interface is assumed.
• dropping the final keyword allows for the rabbit-hole of
  inheritance abuse, like greatly described in this article:
  https://front-line-php.com/object-oriented

I believe I came up with a better idea: what if we could leave both
benefits of prohibiting the inheritance abuse and also allow not to
clutter our namespace with excess entities like interfaces? I hereby
suggest to combine the responsibilities of a class and an interface
into one thing like that:

final class interface C {}
final class D implements C {}

Now other classes can "implement" this class as well. Introduction of
the new syntax (class interface) also solves BC problem - if you
want to forbid your classes to be reimplemented whatsoever, you can
still stick to the final class syntax. Although it is also possible
to allow "reimplementing" ANY class, then new syntax is not needed -
but some library writers like Marco Pivetta could be sad about that I
suppose.

Soo..., what do you think? Could this be a valuable addition to the
language?

This sounds interesting but it breaks some expectations.

Interesting because you can have any class act as an interface for other
classes with the interface being built up of any public properties or
method that exists on that class.
Ok, maybe not any class but just a final class. And also maybe just a final
class that doesn't yet implement an interface.

The expectation it breaks is that if you have a final class, whenever you
use it, you expect some specific implementation exists on it.
And this would break the expectation and in real life someone might pass a
totally different implementation.
Will not break generic LSP but still will break some expectations.

I believe other options should be followed that are more straightforward:

If it's your internal code not shared with others, you can easily extract
an interface at any point where you need to inject another instance (when
testing).
Also, if it's internal code, you can just not mark the class as final.

If it's a library code you use or share with others, a class should not be
marked as final if there is no interface they implement and that should be
fixed by extracting an interface.

If it's a value object, you don't need to mock it, wherever it exists.

Regards,
Alex

Hi again, internals

My marathon of some crazy ideas continues :D, with less crazy one this time.

Idea

Allow "reimplementing" the non-static public API (that is public
properties and methods, excluding constructor) of a class by other
classes like this:

final class interface A {
   public string $s;

   public function __construct(string $s) { $this->s = $s; }

   public static function fromInt(int $i): self { return new
self((string) $i); }

   public function foo(): int { return 42; }
}

final class B implements A {
   public string $s = 'hello';

   public function foo(): int { return 69; }
}

function usesA(A $param): void {}

usesA(new B); // this works

Explanation

Consider there is a class like this:

final class Service {
   public function __construct(private SomeDependency $dependency) {}
   // ...
}

final class SomeDependency {
   // ...
}

We want to write some tests for the Service class, but we don't want
to use a real SomeDependency instance
during tests. A common approach is to either extract an interface
(JUST to make it testable), or to drop the
final keyword and allow extending the class.

Both approaches have their flaws:

• extracting an interface unnecessarily complicates the system, where
  only one "real" implementation of an interface is assumed.
• dropping the final keyword allows for the rabbit-hole of
  inheritance abuse, like greatly described in this article:
  https://front-line-php.com/object-oriented

I believe I came up with a better idea: what if we could leave both
benefits of prohibiting the inheritance abuse and also allow not to
clutter our namespace with excess entities like interfaces? I hereby
suggest to combine the responsibilities of a class and an interface
into one thing like that:

final class interface C {}
final class D implements C {}

Now other classes can "implement" this class as well. Introduction of
the new syntax (class interface) also solves BC problem - if you
want to forbid your classes to be reimplemented whatsoever, you can
still stick to the final class syntax. Although it is also possible
to allow "reimplementing" ANY class, then new syntax is not needed -
but some library writers like Marco Pivetta could be sad about that I
suppose.

Soo..., what do you think? Could this be a valuable addition to the language?

Regards,
Illia / someniatko

--

To unsubscribe, visit: https://www.php.net/unsub.php

Hi

It’s possible I’m missing something here, because it’s hard to tell which parts are new syntax you’re suggesting, and which parts are unfortunate typos…

Can you explain how using a regular interface (or even an abstract base class if you prefer) doesn’t already achieve what you want?

Cheers

Stephen

We want to write some tests for the Service class, but we don't want
to use a real SomeDependency instance
during tests. A common approach is to either extract an interface
(JUST to make it testable), or to drop the
final keyword and allow extending the class.

Both approaches have their flaws:

• extracting an interface unnecessarily complicates the system, where
  only one "real" implementation of an interface is assumed.
• dropping the final keyword allows for the rabbit-hole of
  inheritance abuse, like greatly described in this article:
  https://front-line-php.com/object-oriented

There's another approach that requires neither: removing final
during class loading, for tests only.

See https://github.com/dg/bypass-finals (and
https://github.com/nunomaduro/mock-final-classes for plug'n'play
integration with PHPUnit).