Swift中for in和foreach是遍歷集合的兩種方式，大部分是兩種沒有差別，不過某些特殊情況下有些不一樣。

        let arr: [String] = ["Fly","Elephant","FlyElephant"]
        for item in arr {
            print("\(item)")
        }
        arr.forEach { (item) in
            print("\(item)")
        }

continue 與 break

continue，break只能在for in 循環中使用，foreach如果使用這兩個標簽會報錯。

        let arr: [String] = ["Fly","Elephant","FlyElephant"]
        for item in arr {
            if item == "Fly" {
                continue
            }
            print("\(item)")
        }
        arr.forEach { (item) in
            if item == "Fly" {
                continue
            }
            print("\(item)")
        }

foreach中代碼中會報錯：

'continue' is only allowed inside a loop
 'break' is only allowed inside a loop

return 語句

for in循環中直接返回不會執行之后的代碼，foreach退出當前閉包，但是不會影響迭代的運行。

        let arr: [String] = ["Fly","Elephant","FlyElephant"]
        for item in arr {
            if item == "FlyElephant" {
                return
            }
            print("\(item)")
        }
        print("for in end")
        arr.forEach { (item) in
            if item == "FlyElephant" {
                return
            }
            print("\(item)")
        }
        print("foreach end")

輸出結果:

Fly
Elephant

調整一下代碼順序:

        let arr: [String] = ["Fly","Elephant","FlyElephant"]
        arr.forEach { (item) in
            if item == "FlyElephant" {
                return
            }
            print("\(item)")
        }
        print("foreach end")
        for item in arr {
            if item == "FlyElephant" {
                return
            }
            print("\(item)")
        }
        print("for in end")

輸出結果如下:

Fly
Elephant
foreach end
Fly
Elephant

參考鏈接

https://stackoverflow.com/questions/45333177/when-to-use-foreach-instead-of-for-in