[swift-evolution] Proposal: Deprecate optionals in string interpolation

[Dan Appel]

Optional is already CustomStringConvertible. Again, this was done on
purpose (that's not an argument to keep it this way, though). Source
<https://github.com/apple/swift/blob/master/stdlib/public/core/Optional.swift#L260>

On Wed, May 18, 2016 at 6:33 PM David Sweeris via swift-evolution <
swift-evolution at swift.org> wrote:

> We could make Optional conform to CustomStringConvertible:
> var description: String {
>     switch self {
>         case .some(let x): return "\(x)"
>         case .none: return "\(Wrapped.self)?.none"
>     }
> }
>
> - Dave Sweeris
>
> > On May 18, 2016, at 15:56, Michael Peternell via swift-evolution <
> swift-evolution at swift.org> wrote:
> >
> > Well, I wouldn't deprecate them.
> >
> > Maybe it should print something different: the value itself if it is not
> nil, and "nil" otherwise?
> >
> > Or there may be an optional warning for this case.
> >
> > Or maybe both. But not just deprecate the feature altogether. It will
> make people use the "!" instead in unsafe places (like "\(someOptional!)")
> - it's better not to crash and print something strange instead. Especially
> when in production.
> >
> > -Michael
> >
> >> Am 18.05.2016 um 20:50 schrieb Krystof Vasa via swift-evolution <
> swift-evolution at swift.org>:
> >>
> >> The string interpolation is one of the strong sides of Swift, but also
> one of its weaknesses.
> >>
> >> It has happened to me more than once that I've used the interpolation
> with an optional by mistake and the result is then far from the expected
> result.
> >>
> >> This happened mostly before Swift 2.0's guard expression, but has
> happened since as well.
> >>
> >> The user will seldomly want to really get the output
> "Optional(something)", but is almost always expecting just "something". I
> believe this should be addressed by a warning to force the user to check
> the expression to prevent unwanted results. If you indeed want the output
> of an optional, it's almost always better to use the ?? operator and supply
> a null value placeholder, e.g. "\(myOptional ?? "<<none>>")", or use
> myOptional.debugDescription - which is a valid expression that will always
> return a non-optional value to force the current behavior.
> >>
> >> Krystof
> >>
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> >
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-- 
Dan Appel
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