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12，Subscripts，for Swift 4.0

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kemchenj
2017-09-22 20:21:07 +08:00
parent bc2c9aaef0
commit da73d25416
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source/chapter2/12_Subscripts.md
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@ -14,6 +14,9 @@
> 2.2 > 2.2
> 校对：[SketchK](https://github.com/SketchK) 2016-05-13 > 校对：[SketchK](https://github.com/SketchK) 2016-05-13
> 3.0.1，shanks，2016-11-13 > 3.0.1，shanks，2016-11-13
> 4.0
> 校对：[kemchenj](https://kemchenj.github.io/) 2017-09-21
本页包含内容： 本页包含内容：
@ -111,16 +114,16 @@ struct Matrix {
self.columns = columns self.columns = columns
grid = Array(count: rows * columns, repeatedValue: 0.0) grid = Array(count: rows * columns, repeatedValue: 0.0)
} }
func indexIsValidForRow(row: Int, column: Int) -> Bool { func indexIsValid(row: Int, column: Int) -> Bool {
return row >= 0 && row < rows && column >= 0 && column < columns return row >= 0 && row < rows && column >= 0 && column < columns
} }
subscript(row: Int, column: Int) -> Double { subscript(row: Int, column: Int) -> Double {
get { get {
assert(indexIsValidForRow(row, column: column), "Index out of range") assert(indexIsValid(row: row, column: column), "Index out of range")
return grid[(row * columns) + column] return grid[(row * columns) + column]
} }
set { set {
assert(indexIsValidForRow(row, column: column), "Index out of range") assert(indexIsValid(row: row, column: column), "Index out of range")
grid[(row * columns) + column] = newValue grid[(row * columns) + column] = newValue
} }
} }
@ -150,10 +153,10 @@ matrix[1, 0] = 3.2
![](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Art/subscriptMatrix02_2x.png) ![](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Art/subscriptMatrix02_2x.png)
`Matrix`下标的 getter 和 setter 中都含有断言，用来检查下标入参`row`和`column`的值是否有效。为了方便进行断言，`Matrix`包含了一个名为`indexIsValidForRow(_:column:)`的便利方法，用来检查入参`row`和`column`的值是否在矩阵范围内： `Matrix`下标的 getter 和 setter 中都含有断言，用来检查下标入参`row`和`column`的值是否有效。为了方便进行断言，`Matrix`包含了一个名为`indexIsValid(row:column:)`的便利方法，用来检查入参`row`和`column`的值是否在矩阵范围内：
```swift ```swift
func indexIsValidForRow(row: Int, column: Int) -> Bool { func indexIsValid(row: Int, column: Int) -> Bool {
return row >= 0 && row < rows && column >= 0 && column < columns return row >= 0 && row < rows && column >= 0 && column < columns
} }
``` ```