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.send { color:#77bb77; }
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.error { color:#AA0000; }</style></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div class="bloop_markdown"><p>Besides all that <code>Never</code> as a bottom type means that you can use <code>fatalError()</code> literally everywhere not only on the RHS of <code>??</code>.</p>
<pre><code>func foo(_: Int) {}
foo(fatalError())
</code></pre>
<p>That said, we can kill our application everywhere we would ever imagine, regardless of whether there is <code>?</code> or <code>!</code> operator present somewhere.</p>
<p></p></div><div class="bloop_original_html"><style>body{font-family:Helvetica,Arial;font-size:13px}</style><div id="bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px; color: rgba(0,0,0,1.0); margin: 0px; line-height: auto;"><br></div> <br> <div id="bloop_sign_1498686691508059904" class="bloop_sign"><div style="font-family:helvetica,arial;font-size:13px">-- <br>Adrian Zubarev<br>Sent with Airmail</div></div> <br><p class="airmail_on">Am 28. Juni 2017 um 23:50:18, Jaden Geller via swift-evolution (<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>) schrieb:</p> <blockquote type="cite" class="clean_bq"><span><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div></div><div>
<title></title>
I’m strongly against not using the `??` operator for `x ??
fatalError()` since that is naturally what will be possible once
the `Never` type is a real bottom type. If you want to use `!!` for
the `x !! “bad things!”` convenience form, I don’t care. But the
`Never` form should definitely, definitely use `??`.
<div class=""><br class="">
<div>
<blockquote type="cite" class="">
<div class="">On Jun 28, 2017, at 1:30 PM, Erica Sadun via
swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:</div>
<br class="Apple-interchange-newline">
<div class="">
<div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">
<div class="">Based on the feedback on this thread, I'm coming to
the following conclusions:</div>
<div class=""><br class=""></div>
<div class="">`!!` sends the <i class="">right semantic
message</i>. "Unwrap or die" is an unsafe operation. It is based on
`!`, the unsafe forced unwrap operator, and not on `??`, the safe
fallback nil-coalescing operator. Its symbology should therefore
follow `!` and not `?`. </div>
<div class=""><br class=""></div>
<div class="">The `!!` operator should follow the same semantics as
`<font face="Menlo" style="font-size: 11px;" class="">Optional.unsafelyUnwrapped</font>`, which establishes a
precedent for this approach:</div>
<div class=""><br class=""></div>
<blockquote style="margin: 0 0 0 40px; border: none; padding: 0px;" class="">
<div class="">> "<i class="">The unsafelyUnwrapped property
provides the same value as the forced unwrap operator (postfix !).
However, in optimized builds (-O), no check is performed to ensure
that the current instance actually has a value. Accessing this
property in the case of a nil value is a serious programming error
and could lead to undefined behavior or a runtime error.</i>"</div>
</blockquote>
<div class=""><br class=""></div>
<div class="">By following `<font face="Menlo" style="font-size: 9px;" class="">Optional.unsafelyUnwrapped</font>`, this
approach is consistent with <a href="https://github.com/apple/swift/blob/master/docs/ErrorHandlingRationale.rst#logic-failures" class="">https://github.com/apple/swift/blob/master/docs/ErrorHandlingRationale.rst#logic-failures</a></div>
<div class=""><br class=""></div>
<blockquote style="margin: 0 0 0 40px; border: none; padding: 0px;" class="">
<div class=""><i class=""><span style="font-family: Palatino-Roman;" class="">> "Logic failures are
intended to be handled by fixing the code. It
means </span><span style="font-family: Palatino-Roman;" class="">checks of logic failures can be removed if the code is tested
enough.</span><br style="font-family: Palatino-Roman;" class="">
<span style="font-family: Palatino-Roman;" class="">Actually checks
of logic failures for various operations,
`!`, </span><span style="font-family: Palatino-Roman;" class="">`array[i]`, `&+` and so on, are designed and implemented to
be removed</span><br style="font-family: Palatino-Roman;" class="">
<span style="font-family: Palatino-Roman;" class="">when we use
`-Ounchecked`. It is useful for heavy computation
like </span><span style="font-family: Palatino-Roman;" class="">image processing and machine learning in which overhead of
those </span><span style="font-family: Palatino-Roman;" class="">checks is not permissible."</span></i></div>
</blockquote>
<div class=""><br class=""></div>
<div class="">The right hand side should use a string (or more
properly a string autoclosure) in preference to using a
`<font face="Menlo" style="font-size: 11px;" class="">Never</font>`
bottom type or a `<font face="Menlo" style="font-size: 11px;" class="">() -> Never</font>` closure. A string provides the
cleanest user experience, and allows the greatest degree of
self-documentation. </div>
<div class=""><br class=""></div>
<div class="">- A string is cleaner and more readable to type. It
respects DRY, and avoids using *both* the operator and the call to
`fatalError` or `preconditionFailure` to signal an unsafe
condition:</div>
<blockquote style="margin: 0 0 0 40px; border: none; padding: 0px;" class="">
<div class=""><span style="font-family: Menlo; font-size: 11px;" class="">`let last = array.last !! “Array guaranteed non-empty" //
readable`</span></div>
</blockquote>
<div class="">than: </div>
<blockquote style="margin: 0 0 0 40px; border: none; padding: 0px;" class="">
<div class=""><span style="font-family: Menlo; font-size: 11px;" class="">`let last = array.last !!
fatalError(“Array </span><span style="font-family: Menlo; font-size: 11px;" class="">guaranteed</span><span style="font-family: Menlo; font-size: 11px;" class=""> non-empty”)
// redundant, violates DRY`</span></div>
<div class=""><br class=""></div>
</blockquote>
<div class="">- A string allows the operator *<i class="">itself</i>* to unsafely fail, just as the unary version of `!`
does now. It does this with additional feedback to the developer
during testing, code reading, and code maintenance. The string
provides a self-auditing in-line annotation of the reason why the
forced unwrap has been well considered, using a language construct
to support this.</div>
<div class=""><br class=""></div>
<div class="">- A string disallows a potentially unsafe `Never`
call that does not reflect a serious programming error, for
example:</div>
<blockquote style="margin: 0 0 0 40px; border: none; padding: 0px;" class="">
<div class=""><span style="font-family: Menlo; font-size: 11px;" class="">let last = array.last !! f() //
where </span><span style="font-family: Menlo; font-size: 11px;" class="">func f() ->
Never { while true {} }</span></div>
</blockquote>
<div class=""><br class=""></div>
<div class="">- Although as several list members mention, a `Never`
closure solution is available today in Swift, so is the `!!`
operator solution. Neither one requires a fundamental change to the
language.</div>
<div class=""><br class=""></div>
<div class="">- Pushing forward on this proposal does not in any
way reflect on adopting the still-desirable `Never` bottom
type.</div>
<div class=""><br class=""></div>
<div class="">
<blockquote type="cite" class="">
<div class="">On Jun 28, 2017, at 12:42 PM, Tony Allevato via
swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:</div>
<br class="Apple-interchange-newline">
<div class="">
<div dir="ltr" class=""><br class="">
<br class="">
<div class="gmail_quote">
<div dir="ltr" class="">On Wed, Jun 28, 2017 at 11:15 AM Dave
DeLong <<a href="mailto:delong@apple.com" class="">delong@apple.com</a>> wrote:<br class=""></div>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div style="word-wrap:break-word" class="">
<div class="">
<blockquote type="cite" class="">
<div class="">On Jun 28, 2017, at 10:44 AM, Adrian Zubarev via
swift-evolution <<a href="mailto:swift-evolution@swift.org" target="_blank" class="">swift-evolution@swift.org</a>>
wrote:</div>
<br class="m_-2274859510633634742Apple-interchange-newline">
<div class="">
<div class="">Well the main debate is that, we all want early
access to a feature that will be part of Swift as soon as `Never`
becomes the bottom type. When this happens the `??` will
automatically support the pitched behavior. Until then if we all
agree that we should add it now in a way that will not break
anything we can simply add an overload to `??` as I previously
showed.
<div class=""><br class=""></div>
</div>
</div>
</blockquote>
<div class=""><br class=""></div>
</div>
</div>
<div style="word-wrap:break-word" class="">
<div class="">
<div class="">I believe we should add it now, but I like the recent
observation that making <font face="Menlo" class=""><span style="font-size:11px" class="">??</span></font> suddenly become a
potentially crashing operator violates the expectation that
<font face="Menlo" class=""><span style="font-size:11px" class="">?</span></font> is an indication of safety.</div>
</div>
</div>
</blockquote>
<div class=""><br class=""></div>
<div class="">?? does *not* become a potentially crashing operator.
The *fatalError* (or whatever else the user chooses to put there)
on the right-hand side is the crashing operation.</div>
<div class=""><br class=""></div>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div style="word-wrap:break-word" class="">
<div class="">
<div class=""><br class=""></div>
<div class="">On the other hand, the existing semantics of Swift
are that <font face="Menlo" class=""><span style="font-size:11px" class="">!</span></font> is always dangerous, so making <font face="Menlo" class=""><span style="font-size:11px" class="">!!</span></font> be the a potentially crashing operator is much
more consistent with the language.</div>
</div>
</div>
<div style="word-wrap:break-word" class="">
<div class=""><br class="">
<blockquote type="cite" class="">
<div class="">
<div class="">
<div class="">There is no need for `!!` because it will fade in the
future. If you think of `Never` as a bottom type now then `??` will
already make total sense. The default value for T from rhs might be
T or Never. </div>
</div>
</div>
</blockquote>
<div class=""><br class=""></div>
</div>
</div>
<div style="word-wrap:break-word" class="">
<div class="">
<div class="">I respectfully disagree with your absolute position
on this topic. Even with <font face="Menlo" class=""><span style="font-size:11px" class="">Never</span></font> as a bottom type in
the future, it would <i class="">still</i> be more convenient
for me to type:</div>
<div class=""><br class=""></div>
<div class=""><font face="Menlo" class=""><span style="font-size:11px" class="">let last = array.last !! “Array must be
non-empty"</span></font></div>
<div class=""><br class=""></div>
<div class="">… than it ever would be to type:</div>
<div class=""><br class=""></div>
<div class=""><font face="Menlo" class=""><span style="font-size:11px" class="">let last = array.last ??
fatalError(“Array must be non-empty”)</span></font></div>
</div>
</div>
<div style="word-wrap:break-word" class="">
<div class="">
<div class=""><br class=""></div>
</div>
</div>
</blockquote>
<div class=""><br class=""></div>
<div class="">There is a very high bar for additions to the
standard library—a new operator added to the language is going to
be around (1) forever, or (2) indefinitely with some migration cost
to users if it's ever removed. Shaving off a few keystrokes doesn't
quite meet that bar—especially when an alternative has been shown
to work already that provides the same functionality, is more
general (not coupled to fatalError or String messages), and that
fits better into Swift's design.</div>
<div class=""><br class=""></div>
<div class=""><br class=""></div>
<div class="">To make sure I'm not being too much of a downer, I
would completely support this broader feature being implemented by
that alternative: the ?? + autoclosure () -> Never
combo. Then once Never does become a true bottom type, I believe it
could be removed and the calling code would still *just
work*.</div>
<div class=""><br class=""></div>
<div class=""> </div>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div style="word-wrap:break-word" class="">
<div class="">
<div class=""></div>
<div class="">Dave</div>
</div>
</div>
<div style="word-wrap:break-word" class="">
<div class=""><br class="">
<blockquote type="cite" class="">
<div class="">
<div class="">
<div class=""><br class=""></div>
<div class="">@erica: the rhs argument should be called something
like `noreturnOrError` and not `defaultValue`. And we should keep
in mind that when Never becomes the bottom type we have to remove
that overload from stdlib, because otherwise it will be
ambiguous. </div>
<div class=""><br class=""></div>
<div class="">---</div>
<div class=""><br class=""></div>
<div class="">On the other hand if we tackle a different operator
then we should rething the 'default value operator' because the
second ? signals an optional but not a non-optional or an inplicit
unwrapped operator. In that case I personally thing ?! would make
more sense. Unwrap or (non-optional | IUO | trap/die)<br class="">
<br class="">
<div class="m_-2274859510633634742bloop_sign">
<div style="font-family:helvetica,arial;font-size:13px" class="">
-- <br class="">
Adrian Zubarev<br class="">
Sent with Airmail</div>
</div>
<p class="gmail_quote">Am 28. Juni 2017 um 18:13:18, Tony Allevato
via swift-evolution (<a href="mailto:swift-evolution@swift.org" target="_blank" class="">swift-evolution@swift.org</a>)
schrieb:</p>
<blockquote type="cite" class="gmail_quote">
<div class="">
<div class=""></div>
<div class="">
<div class="">
<div class=""><span class="">It's hard for me to articulate, but
"foo !! message" feels a little too much like a Perl-ism for my
taste. Objectively that's not a great criticism on its own, but I
just don't like the "smell" of an operator that takes a value on
one side and a string for error reporting purposes on the other. It
doesn't feel like it fits the style of Swift. I prefer a version
that makes the call to fatalError (and thus, any other
non-returning handler) explicitly written out in code.<br class="">
<br class="">
So, if the language can already support this with ?? and
autoclosure/Never as was shown above, I'd rather see that added to
the language instead of a new operator that does the same thing
(and is actually less general).</span></div>
</div>
<div class="">
<div class=""><span class=""><br class=""></span>
<div class="gmail_quote">
<div class=""><span class="">On Wed, Jun 28, 2017 at 8:52 AM Jacob
Williams via swift-evolution <<a href="mailto:swift-evolution@swift.org" target="_blank" class="">swift-evolution@swift.org</a>> wrote:<br class=""></span></div>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div style="word-wrap:break-word" class="">
<div class=""><span class="">I feel that the !! operator would be
necessary for indicating that if this fails then something went
horribly wrong somewhere and we should throw the fatalError. This
allows the inclusion of optimizations using -Ounchecked and is
clear that this is an operation that could result in a runtime
error just like force unwrapping.</span></div>
<div class=""><span class=""><br class=""></span></div>
<div class=""><span class="">If we want code clarity and
uniformity, then I think !! Is much better than ?? because it goes
right along with the single ! Used for force unwrapping. However,
this does depend on if the operator would be returning some kind of
error that would cause the program to exit.</span></div>
<div class=""><span class=""><br class=""></span></div>
<div class=""><span class="">I think the ?? operator should not
cause a program to exit early. It goes against optional unwrapping
principles. I think code could get very confusing if some ? would
return nil/a default value, and others would be causing your
program to crash and exit. The ? operators should always be
classified as safe operations.</span></div>
</div>
<div style="word-wrap:break-word" class="">
<div class=""><span class=""><br class=""></span>
<div class="">
<blockquote type="cite" class="">
<div class=""><span class="">On Jun 28, 2017, at 9:41 AM, Ben Cohen
via swift-evolution <<a href="mailto:swift-evolution@swift.org" target="_blank" class="">swift-evolution@swift.org</a>>
wrote:</span></div>
<span class=""><br class="m_-2274859510633634742m_2866777249939610229m_1922728200947037084Apple-interchange-newline">
</span>
<div class="">
<div style="word-wrap:break-word" class=""><span class=""><br class=""></span>
<div class="">
<blockquote type="cite" class="">
<div class=""><span class="">On Jun 28, 2017, at 8:27 AM, David
Hart via swift-evolution <<a href="mailto:swift-evolution@swift.org" target="_blank" class="">swift-evolution@swift.org</a>> wrote:</span></div>
<span class=""><br class="m_-2274859510633634742m_2866777249939610229m_1922728200947037084Apple-interchange-newline">
</span>
<div class=""><span class=""><span style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant-caps:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;float:none;display:inline!important" class="">Count me in as a strong proponent of ?? () -> Never. We
don't need to burden the language with an extra operator just for
that.</span><br class="m_-2274859510633634742m_2866777249939610229m_1922728200947037084Apple-interchange-newline">
</span></div>
</blockquote>
</div>
<br class="">
<div class="">You could say the same about ??</div>
<div class=""><br class=""></div>
<div class="">The concern that an additional operator (and one
that, IMO, fits well into existing patterns) is so burdensome seems
way overweighted in this discussion IMO. </div>
<div class=""><br class=""></div>
<div class="">Adding the operator, and encouraging its use, will
help foster better understanding of optionals and legitimate use of
force-unwrapping in a way that I don’t think `?? fatalError`
could.</div>
<div class=""><br class=""></div>
<div class=""><br class=""></div>
</div>
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_______________________________________________<br>swift-evolution mailing list<br>swift-evolution@swift.org<br>https://lists.swift.org/mailman/listinfo/swift-evolution<br></div></div></span></blockquote></div><div class="bloop_markdown"><p></p></div></body></html>