[swift-evolution] !? operator for ternary conditional unwrapping

[Maxim Veksler]

Thanks for teaching me about .map on Optional. Very cool.

I agree with the comment of $! misleading, maybe a better alternative would
be "??" ?

On Wed, Feb 8, 2017 at 5:12 PM Tony Allevato <tony.allevato at gmail.com>
wrote:

> What you're asking for is already possible (avoiding the optional unwrap)
> by combining map() on Optional with ??:
>
> ```
> let name1: String? = "name"
> print(name1.map { "\"\($0)\"" } ?? "null")  // prints "\"name\""
>
> let name2: String? = nil
> print(name2.map { "\"\($0)\"" } ?? "null")  // prints "null"
> ```
>
> So I guess the question is, does simplifying that rise to the level of
> wanting a custom operator? I personally don't think it does, but I could
> see an argument being made that an operator with defined semantics might be
> a small amount clearer than map + ??. But I think the benefits would have
> to be very strong, though.
>
> And as other folks have mentioned, having "!" in the operator name is
> somewhat misleading, since when I see that I expect a trap to occur in nil
> cases.
>
>
>
> On Wed, Feb 8, 2017 at 6:04 AM Maxim Veksler via swift-evolution <
> swift-evolution at swift.org> wrote:
>
> Hello,
>
> Let's assume I have an optional "name" parameter, based on the optional
> status of the parameters I would like to compose string with either the
> unwrapped value of name, or the string "null". The use case for is
> syntactic sugar to compose a GraphQL queries.
>
> A (sampled) illustration of the code that currently solves it looks as
> following:
>
> func query(name: String?) {
>   let variables_name = name != nil ? "\"\(name!)\"" : "null"
> return "{ param: \(variables_name) }"
> }
>
> Based on optional status the following output is expected
>
> let name = "Max"
> query(name: name)
> // { param: "Max" }
>
> let name: String? = nil
> query(name: name)
> // { param: null }
>
> I think it might be useful to have an conditional unwrap operator !? that
> would enable syntax sugar uch as the following built into the language:
>
> func query(name: String?) {
>   return "{ param: \(name !? "\"\(name)\"": "null") }"
> }
>
> This expression is expected to produce same output as the examples above.
> It means check the Optional state of name: String?, in case it has a
> value, unwrap it and make the unwrapped value accessible under the same
> name to the true condition part of the expression, otherwise return the false
> condition part of the expression.
>
> The effectively removes the need to have the "if != nil" and the forced
> unwrap syntactical code, and IMHO improves code readability and
> expressiveness.
>
> I'm wondering what the community thinks of the displayed use case, and
> proposed solution?
>
>
> -m
>
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