> On Dec 4, 2015, at 10:05 PM, Dmitri Gribenko <griboz...@gmail.com> wrote:
>
> On Fri, Dec 4, 2015 at 10:00 PM, Andrew Trick <atr...@apple.com> wrote:
>> I’m adding runtime functionality to support optional casts and ran into some
>> Optional to String conversion behavior that is currently somewhat
>> accidental—it will break when I add functionality. I want to understand the
>> desired behavior before doing extra work to fix it.
>>
>> Currently swift does this:
>>
>>> print(Int?(3))
>> Optional(3)
>>> print(String?("meow"))
>> Optional("meow")
>>
>> I think swift should do this:
>>
>>> print(Int?(3))
>> 3
>>> print(String?("meow"))
>> "meow"
>>> debugPrint(Int?(3))
>> Optional(3)
>>> debugPrint(String?("meow"))
>> Optional("meow")
>>
>> When a value already knows how to represent itself as a string, I don't
>> think that the string "Optional" belongs in the textual representation.
>>
>> When debugging data structures, it makes sense to include the "Optional"
>> indicator.
>>
>> What was the intention here and what do people think is the desired behavior?
>
> This behavior was not accidental. Here's the rationale:
>
> If an Optional is nil, it should somehow indicate that. Whatever the
> representation is, it would be engineer-oriented and not suitable for
> end users. Thus, Optional should never be printed to users, it would
> only ever be presented to engineers, and thus its print() and
> debugPrint() representations should be the same.
>
> Dmitri
I think you're saying that it's the programmer's responsibility not to
construct a user-visible String from an Optional.
By accidental, I mean that Optional does not conform to
CustomStringConvertible. If we want "Optional" to be part of the string
conversion, then this conformance needs to exist, or I need to add some special
handling of Optional. Do you see any problem with me adding that conformance?
Incidentally, when *do* we want debug string conversion to deviate? Or is it
just a customization point we anticipate to be useful?
Andy
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