> For the complete documentation index, see [llms.txt](https://lochiwei.gitbook.io/ios/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://lochiwei.gitbook.io/ios/swift/flow/loop/for...in-vs.-foreach.md).

# for...in vs. forEach

[Swift](/ios/swift.md) ⟩ [flow control](/ios/swift/flow.md) ⟩ [loop](/ios/swift/flow/loop.md) ⟩ for...in vs. .forEach()

<table><thead><tr><th width="157.33333333333331">flow control</th><th>for ... in</th><th>.forEach()</th></tr></thead><tbody><tr><td><mark style="color:purple;"><strong>continue</strong></mark></td><td>✅ skip to the <mark style="color:red;"><strong>next</strong></mark> iteration.</td><td>⛔ not allowed</td></tr><tr><td><mark style="color:purple;"><strong>break</strong></mark></td><td>✅ break the iteration <mark style="color:red;"><strong>completely</strong></mark>. </td><td>⛔ not allowed</td></tr><tr><td><a data-mention href="/pages/zHYBHx5i0445bpguZAHc">/pages/zHYBHx5i0445bpguZAHc</a></td><td>❌ <mark style="color:red;"><strong>invalid</strong></mark> outside of a <strong>function</strong>.</td><td>❗skip to the <mark style="color:red;"><strong>next</strong></mark> iteration.</td></tr></tbody></table>

{% tabs %}
{% tab title="🧨 雷區" %}

* :point\_right: [replit](https://replit.com/@pegasusroe/forin-vs-forEach#main.swift)

{% hint style="danger" %}
⛔ <mark style="color:red;">**error**</mark>: [return](/ios/swift/flow/transfer/return.md) <mark style="color:red;">**invalid**</mark>**&#x20;**<mark style="color:yellow;">**outside**</mark> of a <mark style="color:blue;">**func**</mark>.
{% endhint %}

```javascript
for n in 1...10 {
    if n == 3 { return }    // ⛔ error
    //          ^^^^^^
    // ⛔ error: return invalid outside of a func
}
```

* :point\_right: [replit](https://replit.com/@pegasusroe/forin-vs-forEach#main.swift)

{% hint style="danger" %}
⛔ <mark style="color:red;">**error**</mark>: [continue](/ios/swift/flow/transfer/continue.md) is <mark style="color:orange;">**only**</mark>**&#x20;**<mark style="color:yellow;">**allowed inside**</mark> a [loop](/ios/swift/flow/loop.md).
{% endhint %}

```javascript
(1...10).forEach { n in 
    if n > 2 { continue }    // ⭐ `continue` is inside a closure❗
    //         ^^^^^^^^
    // ⛔ error: 'continue' is only allowed inside a loop
}
```

* :point\_right: [replit](https://replit.com/@pegasusroe/forin-vs-forEach#main.swift)

{% hint style="danger" %}
⛔ <mark style="color:red;">**error**</mark>: <mark style="color:yellow;">**unlabeled**</mark> [break](/ios/swift/flow/transfer/break.md) is only allowed <mark style="color:yellow;">**inside**</mark> a <mark style="color:orange;">**loop**</mark> or [switch](/ios/swift/flow/branch/switch.md), a <mark style="color:yellow;">**labeled**</mark> [break](/ios/swift/flow/transfer/break.md) is <mark style="color:orange;">**required**</mark> to exit an [if](/ios/swift/flow/branch/if.md) or [do](/ios/swift/statement/do.md).
{% endhint %}

```javascript
(1...10).forEach { n in 
    if n > 2 { break }    // ⭐ `break` is inside a "closure"
    //         ^^^^^
    // ⛔ error: 
    //  • unlabeled 'break' is only allowed inside a loop or switch
    //  • labeled 'break' is required to exit an `if` or `do`
}
```

{% endtab %}

{% tab title="💈範例" %}

* :point\_right: [replit](https://replit.com/@pegasusroe/forin-vs-forEach#main.swift)

```swift
// ------------ for...in ------------------------------

for n in 1...10 {
    if n == 3 { continue }    // ⭐ skip to next iteration
    if n > 6 { break }        // ⭐ break loop completely❗
    a1.append(n)              // [1, 2, 4, 5, 6]
}

// ------------ .forEach ------------------------------

(1...10).forEach { n in 
    if n > 2 { return }     // ⭐ early return ( skip to next iteration❗)
    a2.append(n)            // [1, 2]     (n > 2 NOT appended)
}

(1...10).forEach { n in 
    a3.append(n)            // ⭐ number appended
    if n > 2 { return }     // ⭐ late return ( has no effect❗)
}                           // [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
```

{% endtab %}

{% tab title="⭐️ 重點" %}
{% hint style="info" %}

{% endhint %}
{% endtab %}

{% tab title="👥 相關" %}

* [seq.forEach()](/ios/swift/collections/sequence/seq.foreach.md)
* [for...in](/ios/swift/flow/loop/for...in.md)
  {% endtab %}

{% tab title="📗 參考" %}

* [x] Advanced Swift, p.&#x20;
* [x] Sundell ⟩ [Picking between a for loop and forEach](https://www.swiftbysundell.com/tips/picking-between-for-and-for-each/)
  {% endtab %}
  {% endtabs %}


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