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Date: Tue, 19 Mar 2024 19:38:42 +0000
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Subject: Re: [PHP-DEV] Proposal: AS assertions
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From: imsop.php@rwec.co.uk ("Rowan Tommins [IMSoP]")

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On 19/03/2024 16:24, Robert Landers wrote:
> $x = $attributeReflection->newInstance() as ?MyAttribute;
> if ($x === null) // do something since the attribute isn't MyAttribute


I think reusing nullability for this would be a mistake - ideally, the 
right-hand side should allow any type, so "$foo as ?Foo" should mean the 
same as "$foo as Foo|null".


A better alternative might be to specify a default when the type didn't 
match:

$x = $attributeReflection->newInstance() as ?MyAttribute else null;
if ($x === null) // do something since the attribute isn't MyAttribute

Which then also allows you to skip the if statement completely:

$x = $attributeReflection->newInstance() as MyAttribute else 
MyAttribute::createDefault();


That then looks a lot like a limited-use version of syntax for catching 
an exception inline, which would be nice as a general feature (but I 
think maybe hard to implement?)

$x = somethingThatThrows() catch $someDefaultValue;


As well pattern matching, which Ilija mentioned, another adjacent 
feature is a richer set of casting operators. Currently, we can assert 
that something is an int; or we can force it to be an int; but we can't 
easily say "make this an int if safe, but throw otherwise" or "make this 
an int if safe, but substitute null/$someValue otherwise".

I've been considering how we can improve that for a while, but not 
settled on a firm proposal - there's a lot of different versions we 
*could* support, so choosing a minimal set is hard.


Regards,

-- 
Rowan Tommins
[IMSoP]

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    <div class="moz-cite-prefix">On 19/03/2024 16:24, Robert Landers
      wrote:<br>
    </div>
    <blockquote type="cite"
cite="mid:CAPzBOBMGe=kWWiJYGLG02qxh+2Pe5yTqodhGtAE3LjdAPmkQUw@mail.gmail.com">
      <pre>$x = $attributeReflection-&gt;newInstance() as ?MyAttribute;
if ($x === null) // do something since the attribute isn't MyAttribute</pre>
    </blockquote>
    <p><br>
    </p>
    <p>I think reusing nullability for this would be a mistake -
      ideally, the right-hand side should allow any type, so "$foo as
      ?Foo" should mean the same as "$foo as Foo|null".</p>
    <p><br>
    </p>
    <p>A better alternative might be to specify a default when the type
      didn't match:</p>
    <p>$x = $attributeReflection-&gt;newInstance() as ?MyAttribute else
      null;<br>
      if ($x === null) // do something since the attribute isn't
      MyAttribute</p>
    <p>Which then also allows you to skip the if statement completely:</p>
    <p>$x = $attributeReflection-&gt;newInstance() as MyAttribute else
      MyAttribute::createDefault();</p>
    <p><br>
    </p>
    <p>That then looks a lot like a limited-use version of syntax for
      catching an exception inline, which would be nice as a general
      feature (but I think maybe hard to implement?)</p>
    <p>$x = somethingThatThrows() catch $someDefaultValue;</p>
    <p><br>
    </p>
    <p>As well pattern matching, which Ilija mentioned, another adjacent
      feature is a richer set of casting operators. Currently, we can
      assert that something is an int; or we can force it to be an int;
      but we can't easily say "make this an int if safe, but throw
      otherwise" or "make this an int if safe, but substitute
      null/$someValue otherwise".</p>
    <p>I've been considering how we can improve that for a while, but
      not settled on a firm proposal - there's a lot of different
      versions we *could* support, so choosing a minimal set is hard.<br>
    </p>
    <p><br>
    </p>
    <p>Regards,<br>
    </p>
    <pre class="moz-signature" cols="72">-- 
Rowan Tommins
[IMSoP]</pre>
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