访问和操作数组-添加和删除

在末尾添加

• append(_:) 在末尾添加一个元素
• append(contentsOf:) 在末尾添加多个元素

var numbers = [Int](2...7)
numbers.append(100)
print(numbers)
numbers.append(contentsOf: 100...105)
print(numbers)

运行结果如下：
[2, 3, 4, 5, 6, 7, 100]
[2, 3, 4, 5, 6, 7, 100, 100, 101, 102, 103, 104, 105]

在任意位置插入

• insert(_:at:) 在指定的位置插入一个元素
• insert(contentsOf:at:) 在指定位置插入多个元素

var numbers = [Int](2...7)
numbers.insert(-1, at: 0)
print(numbers)
numbers.insert(contentsOf: -2...0, at: 0)
print(numbers)

运行结果如下：
[-1, 2, 3, 4, 5, 6, 7]
[-2, -1, 0, -1, 2, 3, 4, 5, 6, 7]

字符串也是 Collection

• 字符串也是 Collection, Element 是 Character 类型

var chars:[Character] = ["a","b","c"]
chars.insert(contentsOf: "hello", at: 0)
print(chars)

运行结果如下：
["h", "e", "l", "l", "o", "a", "b", "c"]

移除单个元素

• remove(at:) 移除并返回指定位置的第一个元素
• removeFirst() 移除并返回数组的第一个元素【数组为空时会报错】
• popFirst() 移除并返回数组的第一个元素（optional）【数组为空返回nil】

var chars:[Character] = ["a","b","c","d"]
let removedChar = chars.remove(at: 1)
print(removedChar)
print(chars)

运行结果如下：
b
["a", "c", "d"]

var chars:[Character] = ["a","b","c","d"]
let removedChar = chars.removeFirst()
print(removedChar)
print(chars)

运行结果如下：
a
["b", "c", "d"]

var chars:[Character] = ["a","b","c","d"]
chars.popLast()
print(chars)

运行结果如下：
["a", "b", "c"]

移除多个元素

• removeFirst(:) 移除数组前面多个元素
• removeLast(:) 移除数组后面多个元素

var chars:[Character] = ["a","b","c","d"]
chars.removeFirst(2)
print(chars)

运行结果如下：
["c", "d"]

var chars:[Character] = ["a","b","c","d"]
chars.removeLast(2)
print(chars)

运行结果如下：
["a", "b"]

• removeSubrange(_:) 移除数组中给定范围的元素
• removeAll() 移除数组所有元素
• removeAll(keepingCapacity:) 移除数组所有元素，保留数组容量【建议使用】

var chars:[Character] = ["a","b","c","d"]
chars.removeSubrange(1...2)
print(chars)

运行结果如下：
["a", "d"]

var chars:[Character] = ["a","b","c","d"]
chars.removeAll()
print(chars)
print(chars.capacity)

运行结果如下：
[]
0

var chars:[Character] = ["a","b","c","d"]
chars.removeAll(keepingCapacity: true)
print(chars)
print(chars.capacity)

运行结果如下：
[]
4