It’s worth mentioning that the problem this thread is discussing can be 
generalized to idioms / applicative.  The specific case here is for Optional 
but many other types could benefit from an elegant syntactic solution to this 
problem.  It might be worth exploring a more general solution.  Here’s a link 
to how this is handled in Idris: 


> On Dec 11, 2017, at 12:01 PM, Jared Khan via swift-evolution 
> <> wrote:
> 1. Correct
> 2. It felt natural to me. It’s analogous to the existing optional chaining 
> scenarios and composes nicely. I think it’s about as understandable as 
> existing chaining, a newbie would have to look it up to discover its meaning. 
> What are your thoughts on this particular syntax (ignoring 3. momentarily)? 
> Hopefully others in this thread can share their views too.
> As for how common I’d expect it to be, it’s something I’ve run into myself a 
> few times. Again, I hope members of this list can give their view on if this 
> would be useful to them.
> 3. I’m not entirely sure what the grammar situation is yet but afaik ‘?’ has 
> never been available as a postfix operator. Perhaps I’m missing your point, 
> could you demonstrate where it is allowed?
> Best,
> Jared
>> On 11 Dec 2017, at 17:07, Magnus Ahltorp <> wrote:
>>> 12 Dec. 2017 01:30 Jared Khan via swift-evolution 
>>> <> wrote:
>>> I'd like to propose a syntax addition that acts to ease some things that I 
>>> believe should fall under the umbrella of 'optional chaining'. Optional 
>>> chaining allows us to access the properties of an optional value and return 
>>> nil if any link in that chain breaks. I propose we introduce syntax to 
>>> allow similar chaining when passing optional valued parameters to functions 
>>> that expect that parameter to be non-optional.
>> 1. Am I right in assuming that you propose that the suffix operator "?" 
>> would make the result of the surrounding method/function call optional, so 
>> that a(b(c?)) would make the result of the "b" function call optional, but 
>> not the "a" function call, and that it would be a(b(c?)?) if we would like 
>> to propagate this two levels?
>> 2. If that is the case, is that understandable/neat enough? How common would 
>> you expect this to be?
>> 3. For some reason, (in current Swift) the suffix operator "?" seems to be 
>> allowed in intra-expression syntax, and only fails when the inter-expression 
>> syntax is checked for optionality congruence. Is there a reason for this? I 
>> would have expected that the congruence error "cannot use optional chaining 
>> on non-optional value of type" would never be seen for a lone "?", since the 
>> error message "'?' must be followed by a call, member lookup, or subscript" 
>> would always be displayed first if it was checked first. The "." operator 
>> checks intra-expression syntax first, before checking congruence. Is this a 
>> sign that "?" as a suffix operator is already somewhat operational as an 
>> operator for optional types? I have a faint recollection that it was doing 
>> something in earlier versions of Swift.
>> /Magnus
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