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Swift 2017-03-29 18:53

@Daniel

I have difficulty to open the site that you said.

是的，需要用VPN才行。

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Daniel 2017-04-01 01:25

@Swift

@Daniel

I have difficulty to open the site that you said.

是的，需要用VPN才行。

What is VPN?

Your quoted site https://swift.sandbox.bluemix.net/#/repl will work on the following browers:

360極速瀏覽器, 2144瀏覽器, Google Chrome瀏覽器, 搜狗高速瀏覽器及 UC瀏覽器.

Thank you very much.

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Swift 2017-04-01 11:36

@Daniel 你能訪問就好。這里說的VPN指網(wǎng)絡(luò)代理，幫你訪問一些比較慢或無法訪問的網(wǎng)站。

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Daniel 2017-04-02 23:29

Since you have learned Swift (編程語言) more than a couple of years already, what suggestions and guidance will you give me for learning the language?

My first and current reading is [The Swift Programming Language (Swift 3.1)] with the help of the IBM Swift Sandbox interpreter. What else will you suggest?

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Swift 2017-04-04 17:16

我2014年開始接觸Swift，那時(shí)也只是學(xué)了點(diǎn)基礎(chǔ)語法，沒有學(xué)習(xí)iOS的開發(fā)，而且現(xiàn)在語法有變動(dòng)，還得重新學(xué)習(xí)。所以我跟你一樣是個(gè)新手，所以目前給不了你什么建議。
后續(xù)網(wǎng)站會(huì)更新一些視頻教程，希望能夠?qū)δ阌杏谩?

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Daniel 2017-04-05 22:51

@Swift

我2014年開始接觸Swift，那時(shí)也只是學(xué)了點(diǎn)基礎(chǔ)語法，沒有學(xué)習(xí)iOS的開發(fā)，而且現(xiàn)在語法有變動(dòng)，還得重新學(xué)習(xí)。所以我跟你一樣是個(gè)新手，所以目前給不了你什么建議。
后續(xù)網(wǎng)站會(huì)更新一些視頻教程，希望能夠?qū)δ阌杏谩?

I tried the sample code in [Subscript Options] of [The Swift Programming Language (Swift 3.1)], I had compilation errors.

Can you help debugging ?

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Swift 2017-04-05 23:23

@Daniel 把代碼發(fā)出來看看（通過點(diǎn)擊紅色的Swift圖標(biāo)插入程序代碼），我試一下看會(huì)不會(huì)出錯(cuò)。

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Daniel 2017-04-06 05:35

struct Matrix {
    let rows: Int, columns: Int
    var grid: [Double]
    init(rows: Int, columns: Int) {
        self.rows = rows
        self.columns = columns
        grid = Array(repeating: 0.0, count: rows * columns)
    }
    func indexIsValid(row: Int, column: Int) -> Bool {
        return row >= 0 && row < rows && column >= 0 && column < columns
    }
    subscript(row: Int, column: Int) -> Double {
        get {
            assert(indexIsValid(row: row, column: column), "Index out of range")
            return grid[(row * columns) + column]
        }
        set {
            assert(indexIsValid(row: row, column: column), "Index out of range")
            grid[(row * columns) + column] = newValue
        }
    }
}
var matrix = Matrix(rows: 2, columns: 2)
matrix[0, 1] = 1.5
matrix[1, 0] = 3.2
func indexIsValidForRow(row: Int, column: Int) -> Bool {
    return row >= 0 && row < rows && column >= 0 && column < columns
}
let someValue = matrix[2, 2]
// this triggers an assert, because [2, 2] is outside of the matrix bounds

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Swift 2017-04-08 13:10

@Daniel 之前用Xcode7.1編譯出錯(cuò)，今天裝了個(gè)Xcode8.3，indexIsValidForRow函數(shù)放到Matrix結(jié)構(gòu)體中就可以了。修改的代碼如下：

struct Matrix {
    let rows: Int, columns: Int
    var grid: [Double]
    init(rows: Int, columns: Int) {
        self.rows = rows
        self.columns = columns
        grid = Array(repeating: 0.0, count: rows * columns)
    }
    func indexIsValid(row: Int, column: Int) -> Bool {
        return row >= 0 && row < rows && column >= 0 && column < columns
    }
    subscript(row: Int, column: Int) -> Double {
        get {
            assert(indexIsValid(row: row, column: column), "Index out of range")
            return grid[(row * columns) + column]
        }
        set {
            assert(indexIsValid(row: row, column: column), "Index out of range")
            grid[(row * columns) + column] = newValue
        }
    }
    
    func indexIsValidForRow(row: Int, column: Int) -> Bool {
        return row >= 0 && row < rows && column >= 0 && column < columns
    }
}
var matrix = Matrix(rows: 2, columns: 2)
matrix[0, 1] = 1.5
matrix[1, 0] = 3.2

let someValue = matrix[1, 1]
// let someValue = matrix[2, 2]
// this triggers an assert, because [2, 2] is outside of the matrix bounds

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Daniel 2017-04-09 18:25

You are great!

Recently I bought 3 electronic books, but I will wait to read them until I purchase a new Mac Pro next year when it is available. 蘋果Mac Pro垃圾桶最低配的ME253CH

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Swift 2017-04-11 20:13

你這還要等很久啊，明年就得學(xué)Swift4了。

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Daniel 2017-04-12 08:16

I have no need to rush. I don't want to buy a current Mac Pro which will not be manufactured soon because a future Mac Pro is completely different from a current one. It is difficult to get the current model repaired in the future due to the eventual lack of its spare parts.
Also I need to spend about RMB50,000 to fix my teeth this year.

dkychang@qq.com

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Swift 2017-04-12 22:10

是的，不急的話可以等下，就像iPhone8一樣，值得期待。

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Daniel 2017-04-24 10:17

Functions are a first-class type. This means that a function can return another function as its value:

func makeIncrementer() -> ((Int) -> Int) {
    func addOne(number: Int) -> Int {
        return 1 + number
    }
    return addOne
}
var increment = makeIncrementer()
print(increment(7))

Swift is not easy, I don't understand the above code. Do you?

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Swift 2017-04-24 13:16

//返回addOne這個(gè)函數(shù)
func makeIncrementer() -> ((Int) -> Int) {
    func addOne(number: Int) -> Int {
        return 1 + number
    }
    return addOne
}

//increment存放makeIncrementer()返回的函數(shù)，即increment就是addOne()
var increment = makeIncrementer()

//實(shí)際就是調(diào)用了addOne()，輸出結(jié)果為8
print(increment(7))

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Daniel 2017-04-24 20:12

I still don't understand.

Why increment can take an argument?

makeIncrementer () takes NO argument.

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Swift 2017-04-24 22:02

因?yàn)閕ncrement是addOne，addOne是帶參數(shù)的；makeIncrementer()定義時(shí)就時(shí)沒有參數(shù)。

你不要把increment當(dāng)成makeIncrementer()，increment只是makeIncrementer()返回的一個(gè)函數(shù)。在Java中可以理解為increment是makeIncrementer()返回的一個(gè)對(duì)象，區(qū)別就是在于在Java中函數(shù)不是class，而Swift中函數(shù)也算是class，所以在Swift中可以把一個(gè)函數(shù)作為返回值，也可以作為參數(shù)。

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Daniel 2017-04-28 08:55

func anyCommonElements<T: Sequence, U: Sequence>(_ lhs: T, _ rhs: U) -> Bool
    where T.Iterator.Element: Equatable, T.Iterator.Element == U.Iterator.Element {
        for lhsItem in lhs {
            for rhsItem in rhs {
                if lhsItem == rhsItem {
                    return true
                }
            }
        }
        return false
}
anyCommonElements([1, 2, 3], [3])

Another piece of code that I don't understand, maybe you can explain?

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Swift 2017-04-29 17:47

//這個(gè)函數(shù)是用于判斷兩個(gè)數(shù)組中是否有相同元素
//<T: Sequence, U: Sequence> 這里用了泛型，指定了參數(shù)T和U的類型必須實(shí)現(xiàn)Sequence協(xié)議，即參數(shù)必須是數(shù)組或集合等可遍歷的
func anyCommonElements<T: Sequence, U: Sequence>(_ lhs: T, _ rhs: U) -> Bool
    //where子句是對(duì)泛型對(duì)參數(shù)T和U做了約束，調(diào)用函數(shù)時(shí)傳遞的參數(shù)達(dá)到以下2個(gè)條件才行
    //T.Iterator.Element: Equatable 參數(shù)T必須實(shí)現(xiàn)Equatable協(xié)議，實(shí)現(xiàn)Equatable協(xié)議的類型才可以使用 == 和 != 進(jìn)行比較
    //T.Iterator.Element == U.Iterator.Element 這句要求T和U的類型必須是相同的，例：要么都是字符，要么都是數(shù)字。
    where T.Iterator.Element: Equatable, T.Iterator.Element == U.Iterator.Element {
        
        //這里就是循環(huán)對(duì)比內(nèi)容了，一旦發(fā)現(xiàn)有相同的元素則返回true
        for lhsItem in lhs {
            for rhsItem in rhs {
                if lhsItem == rhsItem {
                    return true
                }
            }
        }
        return false
}

//這里結(jié)果是true，因?yàn)閮蓚€(gè)數(shù)組中都有3
anyCommonElements([1, 2, 3], [3, 4])


//上面調(diào)用時(shí)參數(shù)時(shí)用的數(shù)字，下面例子使用的字符，其它實(shí)現(xiàn)Equatable協(xié)議的類型也可以使用。
//這里結(jié)果是false
anyCommonElements(["1", "2"], ["3", "7"])

//總結(jié)：泛型可以使同一個(gè)函數(shù)，支持多種類型，而不需要為不同類型分別寫一個(gè)函數(shù)。

關(guān)于泛型可以參考：泛型 - Swift 3.0 教程

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Daniel 2017-04-30 06:38

I know the results of the examples because I tried the IBM compiler. But the terms (Sequence, Iterator and Equatable) have never been explained in the document [The Swift Programming Language (Swift 3.1)]?

Have you read other documents?

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