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

Adrian Zubarev adrian.zubarev at devandartist.com
Wed Feb 8 08:52:21 CST 2017

You could always write something like this:

func query(name: String?) -> String {
    let variables_name = String(format: name == nil ? "%@" : "\"%@\"", name ?? "null")
    return "{ param: \(variables_name) }"

query(name: "Max") //=> "{ param: "Max" }"
query(name: nil)   //=> "{ param: null }"
As far as I’m concerned, string interpolation in Swift does not allow nested string literals (yet).

But a ternary operator that could potentially unwrap a list of optional values would be neat.


(optional1, optional2, optional1) ? { tupleWithUnwrappedOptionals in return R } : { R }

// variadic generic parameter list
ternary func ?: <…T, R>(list: (…T?), lhs: ((…T) -> R), rhs: () -> R) -> R {
    if let unwrappedList = // unwrap all optionals in `list` {
        return lhs(unwrappedList)
    } else {
        return rhs()

Adrian Zubarev
Sent with Airmail

Am 8. Februar 2017 um 15:04:44, Maxim Veksler via swift-evolution (swift-evolution at swift.org) schrieb:


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?) {
variables_name = name != nil ? "\"\(name!)\"" :

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?) {
"{ 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

I'm wondering what the community thinks of the displayed use case, and proposed solution?

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