CODEWITHSUNDEEP
iosswift
progammingBeignner
progammingBeignner

Reputation: 936

Closure as constructor?

I have seen an example on objc io book like this 

callback(Result {
    if let e = error {
       throw e
    }

    guard let d = data else {
       throw NoDataError()
    }

    return try JSONDecoder().decode(User.self, from: d)
})

where callback is 

“callback: @escaping (Result<User, Error>) -> ()

It seems that Result, which is an enum type as defined by Swift is using a closure to create itself?

But i don see any documentation on this

Upvotes: 2

Views: 710

Answers (1)

vadian
vadian

Reputation: 285072

There is a documentation.

The expression represents the trailing closure syntax of the init(catching:) method of Result. The description is

Creates a new result by evaluating a throwing closure, capturing the returned value as a success, or any thrown error as a failure.

The full syntax is

callback(Result(catching: {
    if let e = error { 
       throw e 
    }

    guard let d = data else { 
       throw NoDataError() 
    }

    return try JSONDecoder().decode(User.self, from: d)
    })
)

Please see also Preserving the Results of a Throwing Expression

Upvotes: 3

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