// 不可变数组 不能.append()等
let keepArray = [5, 3, 2, 4, 1, 6]
 
 
// 过滤数组元素
let keepArray2 = keepArray.filter { element in
    element > 3
}
for item in keepArray2 {
    print(item) // 5 4 6
}
print("-------------------")
 
 
// 替换数组中的元素
let keepArray3 = keepArray.map { element in
    return 1
}
 
for item in keepArray3 {
    print(item) // 1 1 1 1 1 1
}
print("-------------------")
 
 
// 数组元素排序
let keepArray4 = keepArray.sorted()
 
for item in keepArray4 {
    print(item) // 1 2 3 4 5 6
}
print("-------------------")
// keepArray 始终没变 filter  map  sorted 都是生成的新数组
 
//
print(keepArray.last ?? 0) // 6
print(keepArray.first ?? 0)// 5
print(keepArray.startIndex)// 0
print(keepArray.endIndex)// 6  注意这个并不是最后一个索引
print(keepArray.count)// 6
print("-------------------")
 
 
 
 
 
// 可变数组 能.append()等
var mutableArray = [Int]()
 
// 数组拼接
mutableArray = mutableArray + keepArray
mutableArray += keepArray
// CURD数组元素
mutableArray.append(123) // 增
mutableArray.remove(at: 0) // 删
mutableArray[0] = 567 // 改
print(mutableArray[0]) // 查 567
 
print(mutableArray)// [567, 2, 4, 1, 6, 5, 3, 2, 4, 1, 6, 123]