Swift 4 减少问题 : Cannot use mutating member on immutable value: function call returns immutable value

Question

我被困在一个

Cannot use mutating member on immutable value: function call returns immutable value

这段代码错误:

var bagsToScan: [BagQR] {
    var initial: [Bag] = []
    return TaskManager.shared.tasks.value
        .filter({ $0.state == .ready })
        .reduce(initial) { (acc, task) in
            var bagQR = task.bags.filter({
                !tasksChecked.contains(BagQR(bag: $0, taskName: task.name).taskName)
            }).map({
                BagQR(bag: $0, taskName: task.name)
            })

            acc.append(contentsOf: bagQR)
        }.sort({ $0.bag.scanIndex < $1.bag.scanIndex })
}

错误打印在 reduce(initial) { (acc, task) in 行中。感谢您的帮助!

Answer 1

使用reduce(into:_:)

.reduce(into: initial) { (acc, task) in
//...

这将使 acc 可变。

并使用 sorted(by:)关于 reduce 的结果。

.sorted(by: { $0.bag.scanIndex < $1.bag.scanIndex })