Question

我正在尝试在Swift中创建一个Matrix类，但我在self.data[row * columns..<(row + 1) * columns] = data函数的setRow()行上收到错误。错误是'无法指定类型'[Double]'的值来键入'ArraySlice''

struct Matrix: CustomStringConvertible {
    let rows:Int
    let columns:Int
    var data:[Double]

    // Description
    public var description: String {
        var description = ""
        for r in 0..<rows {
            description += data[r * columns..<(r + 1) * columns].description + "\n"
        }
        return description
    }

    // Initialisation
    init(rows: Int, columns: Int) {
        self.rows = rows
        self.columns = columns
        self.data = Array(repeating: 0.0, count: rows * columns)
    }

    init(rows: Int, columns: Int, data:[Double]) {
        assert(data.count == (rows * columns),"Number of elements must equal rows * columns")
        self.rows = rows
        self.columns = columns
        self.data = data
    }

    // Validity
    func validRow(row: Int) -> Bool {
        return row > 0 && row < rows
    }

    func validColumn(column: Int) -> Bool {
        return column > 0 && column < columns
    }

    func validIndex(row: Int, column: Int) -> Bool {
        return validRow(row: row) && validColumn(column: column)
    }

    // Setters and getters
    func get(row: Int, column: Int) -> Double {
        assert(validIndex(row: row,column: column), "Index out of range")
        return data[(row * columns) + column]
    }

    mutating func set(row: Int, column: Int, value: Double) {
        assert(validIndex(row: row,column: column), "Index out of range")
        data[(row * columns) + column] = value
    }

    func getRow(row: Int) -> [Double] {
        assert(validRow(row: row), "Index out of range")
        return Array(data[row * columns..<(row + 1) * columns])
    }

    mutating func setRow(row: Int, data:[Double]) {
        assert(validRow(row: row), "Index out of range")
        assert(data.count == columns, "Data must be same length ans the number of columns")
        self.data[row * columns..<(row + 1) * columns] = data
    }

    // Swapping
    mutating func swapRow(row1: Int, row2: Int) {
        assert(validRow(row: row1) && validRow(row: row2), "Index out of range")
        let holder = getRow(row: row2)
        setRow(row: row2, data: getRow(row: row1))
        setRow(row: row1, data: holder)
    }
}

Answer 1

正如错误所述，Array的远程下标涉及ArraySlice，而不是Array。

一个解决方案，如@vacawama says，只是创建整个输入数组的一个切片。这可以通过下标数组indices：

来完成

mutating func setRow(row: Int, data newData: [Double]) {
    assert(validRow(row: row), "Index out of range")
    assert(data.count == columns, "Data must be same length ans the number of columns")
    data[row * columns ..< (row + 1) * columns] = newData[newData.indices]
}

或者在Swift 4中，您可以利用the ... 'operator'，它完全相同：

data[row * columns ..< (row + 1) * columns] = newData[...]

但IMO是一个更好的工具，可以replaceSubrange(_:with:)：

mutating func replaceSubrange<C>(_ subrange: Range<Int>, with newElements: C) 
     where Element == C.Element, C : Collection

因为它允许您处理任意Collection个新元素，这意味着您还可以使setRow通用：

mutating func setRow<C : Collection>(row: Int, data newData: C)
    where C.Iterator.Element == Double { // <- in Swift 4, remove ".Iterator"

    assert(validRow(row: row), "Index out of range")
    assert(data.count == columns, "Data must be same length ans the number of columns")
    data.replaceSubrange(row * columns ..< (row + 1) * columns, with: newData)
}

Answer 2

听起来很简单。您是不是想在功能中仅设置Double而不是[Double]？

mutating func setRow(row: Int, data: Double) {
        assert(validRow(row: row), "Index out of range")
        assert(data.count == columns, "Data must be same length ans the number of columns")
        self.data[row * columns..<(row + 1) * columns] = data
    }

Swift：在struct中变异数组

2 个答案: