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To: Joe Watkins <pthreads@pthreads.org>,
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Date: Thu, 28 Apr 2016 21:42:50 +0200
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Subject: Re: Fwd: [PHP-DEV] [RFC] PHP Attributes
From: php@fleshgrinder.com (Fleshgrinder)

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From: Fleshgrinder <php@fleshgrinder.com>
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Subject: Re: Fwd: [PHP-DEV] [RFC] PHP Attributes
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Is there a reason why you think that Design by Contract (DbC) should be
implemented via annotations/attributes?

I personally think that such a system should be implemented directly in
the language, like Eiffel has it. I even think that it would be easy to
add it without any BC. It might be a bit more complicated to implement
thought.

  [assert]
  assert.active    =3D 1
  assert.invariant =3D 1
  assert.require   =3D 1 ; preconditions
  assert.ensure    =3D 1 ; postconditions

  class PreconditionError extends AssertionError {}
  class PostconditionError extends AssertionError {}

  function hello(string $who): string {
    return "Hello {$who}\n";
  }
  require {
    # argument must have content
    $who !=3D=3D '';
    # argument cannot contain unprintable characters
    ctype_print($who);
  }

  hello('');
  // PHP Warning: require(): argument must have content: "$who !=3D=3D ''=
"
  // failed in ...

  hello("\0");
  // PHP Warning: require(): argument cannot contain unprintable
  // characters: "ctype_print($who)" failed in ...

  class A {

    private DateTimeImmutable $created;
    private DateTimeImmutable $changed;

    function f() {}
    require {}
    // Special scope "old" available...
    ensure {
      # error message
      $this->x =3D old::$x - 42;
    }

  }
  ensure {
    # created cannot be less than changed time
    $this->created <=3D $this->changed;
  }

--=20
Richard "Fleshgrinder" Fussenegger


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