具有显式参数的闭包内部不能使用匿名闭包 [英] Anonymous closure can not be used inside a closure that has explicit arguments

问题描述

smb可以解释什么问题吗，应该如何修改代码？

Can smb explain what is the problem, how should I modify my code?

我需要过滤 CKRecord s从 CloudKit 返回。

I need to filter CKRecords returned from CloudKit.

override func tableView(tableView: UITableView, moveRowAtIndexPath sourceIndexPath: NSIndexPath, toIndexPath destinationIndexPath: NSIndexPath) {

    let defaultContainer = CKContainer.defaultContainer()
    let publicDatabase = defaultContainer.publicCloudDatabase

    let myfunc2 = myfunc(names, { (records: [CKRecord], error: NSError) in
        if error == nil {

            let records2 = records.filter($0.value > sourceIndexPath.row && $0.value < destinationIndexPath.row)

            let mro = CKModifyRecordsOperation(recordsToSave: [], recordIDsToDelete: [])

        } else {

        }
    })

推荐答案

编写闭包的方法有两种：使用显式参数名称，或将参数称为$ 0， $ 1等。

There are two ways to write closures: with explicit argument names, or by referring to the arguments as $0, $1 etc.

例如，这两件事是等效的：

For example, these two things are equivalent:

// implicit argument names, $0 and $1
let x = reduce(1...5, 0) { $0 + $1 }

// explicit argument names i and j
let y = reduce(1...5, 0) { i, j in i + j }

但是您不能混合使用这些东西–您可以命名参数，或者使用 $ n 。您不能同时做这两个事情：

But you can’t mix these things – either you name the arguments, or you use $n. You can’t do both:

// name the arguments, but still use $0 and $1
let x = reduce(1...5, 0) { $0 + $1 }
// compiler error: Anonymous closure arguments cannot be used
// inside a closure that has explicit arguments

在您的示例中，您似乎忘记了为过滤器提供闭包方法。这意味着您的 $ 0 不在没有参数的新闭包中–因此Swift编译器认为您的 $ 0 是指外部闭包将其参数明确命名为记录和错误。因此，它抱怨您不能在带有显式参数名称的闭包内将参数称为 $ 0 。

In your example, it looks like you’ve forgotten to supply a closure to the filter method. This means your $0 isn’t inside a new closure without arguments – so the Swift compiler thinks your $0 is referring to the outer closure that names it’s arguments explicitly as records and error. So it’s complaining you can’t refer to arguments as $0 inside a closure with explicit argument names.

（当然，修复程序实际上是提供 filter 的闭包，即用替换您的（） { } ）

(the fix is of course to actually supply a closure to filter i.e. replace your () with {})

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