> On 11 Oct 2016, at 07:16, Karl wrote:
>
> You might expect this code to work:
>
> func aFunction() -> Int? { return 5 }
> func bFunction() throws -> Int { return 4 }
>
> let value = aFunction() ?? try bFunction() // ERROR: Operator can throw but
> expression is not marked with a ‘try'
> print(value)
>
> Instead, you must put the ‘try’ before the entire expression:
>
> let value = try aFunction() ?? bFunction()
>
> This is awkward, since aFunction() doesn’t throw.
> I propose we change the grammar to allow the first example and disallow the
> second, consistent with the idea that throwing calls are ‘marked’ by using
> the try keyword.
The `??` function rethrows an error from its rhs operand.
@_transparent
public func ?? <T>(optional: T?, defaultValue: @autoclosure () throws
-> T)
rethrows -> T {
switch optional {
case .some(let value):
return value
case .none:
return try defaultValue()
}
}
<https://github.com/apple/swift/blob/5d3a7f7c230ae238c848a06f58b58c7e68fb5ed0/stdlib/public/core/Optional.swift#L415-L424>
-- Ben
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