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Date: Sat, 22 Jun 2024 20:26:39 +0100
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Subject: Re: [PHP-DEV] [Early Feedback] Pattern matching
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From: imsop.php@rwec.co.uk ("Rowan Tommins [IMSoP]")

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On 22/06/2024 19:34, Robert Landers wrote:
> I've brought this up before, but I mostly see "as" being useful for
> static analysis. That's what I've mostly used it for C#, anyway.
> Logically, you know the type, but due to one-thing-or-another you
> can't "prove" the type is that type (such as foreach-arrays or dealing
> with results from user-code callbacks in library code). I want to be
> able to say "this is an int or else."


I absolutely see the use case for that; I just don't think "as" is a 
good word for it, because that's not what it means in normal English.


Incidentally, according to the C# docs at 
https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/operators/type-testing-and-cast#as-operator

 > The as operator explicitly converts the result of an expression to a 
given reference or nullable value type. If the conversion isn't 
possible, the as operator returns null. Unlike a cast expression, the as 
operator never throws an exception.

So it more closely matches my intuition: a statement of just "foo as 
Bar;" would be useless, because it's calculating a value and discarding 
it, with no side effects.

As you say, the conversion might not be of the value, but of the 
statically analysed type, but in C#, that's all part of the language. In 
PHP "$foo = $bar as SomeInterface;" would have no visible effect except 
in third-party tooling, where it can already be written "/** @var 
SomeInterface $foo */ $foo = $bar;"


-- 
Rowan Tommins
[IMSoP]

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    <div class="moz-cite-prefix">On 22/06/2024 19:34, Robert Landers
      wrote:<br>
    </div>
    <blockquote type="cite"
cite="mid:CAPzBOBOwAbR=3cbyQxgYbnBEGcoJbkReOYVTsrd0ojBbZbf=ng@mail.gmail.com">
      <pre>I've brought this up before, but I mostly see "as" being useful for
static analysis. That's what I've mostly used it for C#, anyway.
Logically, you know the type, but due to one-thing-or-another you
can't "prove" the type is that type (such as foreach-arrays or dealing
with results from user-code callbacks in library code). I want to be
able to say "this is an int or else."</pre>
    </blockquote>
    <p><br>
    </p>
    <p>I absolutely see the use case for that; I just don't think "as"
      is a good word for it, because that's not what it means in normal
      English.</p>
    <p><br>
    </p>
    <p>Incidentally, according to the C# docs at
<a class="moz-txt-link-freetext" href="https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/operators/type-testing-and-cast#as-operator">https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/operators/type-testing-and-cast#as-operator</a></p>
    <p>&gt; The as operator explicitly converts the result of an
      expression to a given reference or nullable value type. If the
      conversion isn't possible, the as operator returns null. Unlike a
      cast expression, the as operator never throws an exception.</p>
    <p>So it more closely matches my intuition: a statement of just "foo
      as Bar;" would be useless, because it's calculating a value and
      discarding it, with no side effects.<br>
    </p>
    <p>As you say, the conversion might not be of the value, but of the
      statically analysed type, but in C#, that's all part of the
      language. In PHP "$foo = $bar as SomeInterface;" would have no
      visible effect except in third-party tooling, where it can already
      be written "/** @var SomeInterface $foo */ $foo = $bar;"<br>
    </p>
    <p><br>
    </p>
    <pre class="moz-signature" cols="72">-- 
Rowan Tommins
[IMSoP]</pre>
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