Array

通过查看Collection>Array学习相关属性知识

• capacity 当前数组最大承载能力

  数组初始化后，会默认分配一块大于或等于array.count数的使用,如果当前capacity>= count, 增加新数据时，则不去开辟新内存存储数据，直到所有空间将要用完

  
  WeChat001e43b6f1da1fb5b2b9291c311b9a38.png

• replaceSubrange 替换数组

  根据range替换数组中数据,range长度随意

  
  WeChate3288dcb7d11b75c8933a61d9961b6cb.png

• popLast 删除最后一个元素

  与removeLast()的区别为：remove不支持空数组删除，poplast支持;
  popFirst也就清楚怎么用了😁

• dropLast 从数组末尾开始删除，并返回删除后的新数组

var numbers = [10, 20, 30, 40]
numbers.append(contentsOf:stride(from: 50, through: 100, by: 10))
print("\t\t剩余数组为：\(numbers.dropLast(5))")  //剩余数组为：[10, 20, 30, 40, 50]

• suffix 与droplast功能相反

如输入的k值大于数组长度，返回数组本身

var numbers = [10, 20, 30, 40]
numbers.append(contentsOf:stride(from: 50, through: 100, by: 10))
print("\t\t剩余数组为：\(numbers.suffix(5))")  //剩余数组为：[60, 70, 80, 90, 100]
print("\t\t剩余数组为：\(numbers.suffix(15))")  //剩余数组为：[10, 20, 30, 40, 50, 60, 70, 80, 90, 100]

• map 数组映射为另外一个数组

let numbers = [10, 20, 30, 40]
numbers.map { $0/10 }
print("\t\t剩余数组为：\(numbers.map { $0/10 })")  //剩余数组为：[1, 2, 3, 4]
print("\t\t剩余数组为：\(numbers.map{String($0)})")  //剩余数组为：["10", "20", "30", "40"]

• drop 根据闭包条件删除数据，如闭包中返回false，则马上停止。

let numbers = [10, 20, 30, 40]
print("\t\t剩余数组为：\(numbers.drop(while: { $0 >= 20 }))")  //剩余数组为：[10, 20, 30, 40]。由于$0=10时，不满足>=20，跳出closure，返回数组本身
print("\t\t剩余数组为：\(numbers.drop(while: { $0 < 20 }))") //剩余数组为：[20, 30, 40].  小于20的数据被删除

• prefix(maxLength)、prefix(upTo:)返回数组前缀

测试使用时候，两方法返回对象一致，目前发现的差别是：maxlength>array.count时，返回本身； upTo>array.count时，编译报错

let numbers = [10, 20, 30, 40]
print("\t\t剩余数组为：\(numbers.prefix(8))")  //剩余数组为：[10, 20, 30, 40]
print("\t\t剩余数组为：\(numbers.prefix(upTo: 8))") //Fatal error: Array index is out of range

• split字符串拆分为数组

let line = "BLANCHE:   I don't want realism. I want magic!"
print(line.split(whereSeparator: { $0 == " " })) //["BLANCHE:", "I", "don\'t", "want", "realism.", "I", "want", "magic!"]
print(line.split(maxSplits: 2, whereSeparator: { $0 == " " }))//["BLANCHE:", "I", "don\'t want realism. I want magic!"]
print(line.split(omittingEmptySubsequences: false, whereSeparator: { $0 == " " }))//["BLANCHE:", "", "", "I", "don\'t", "want", "realism.", "I", "want", "magic!"]

数组拆分为字符串也可以使用此方法，但是有一点需要注意，Array与ArraySlice需要进行转化,当为ArraySlice时，通过subscript方式访问会失败,如a为ArraySlice，a[0],时将得到:Fatal error: Index out of bounds