🍎 Swift Array Slices – Complete Tutorial

In Swift Array Slices lets you extract a portion of an array without copying all elements.
Slices are efficient, safe, and commonly used in iOS/macOS development and interviews.

1️⃣ What is an Array Slice in Swift?

An Array Slice:

• Is a view into an existing array

• Uses a range of indices

• Does not copy data (memory efficient)

• Type is ArraySlice<Element>, not Array<Element>

2️⃣ Creating an Array Slice ⭐

Using Closed Range (...)

Using Half-Open Range (..<)

3️⃣ Type of Array Slice ⭐ (Very Important)

📌 Interview trap: Slice is NOT an Array.

4️⃣ Looping Through an Array Slice ⭐

✔ Works just like an array

5️⃣ Accessing Slice Elements ⚠️

Array slices keep original indices.

❌ This may surprise beginners:

📌 Indices are inherited from original array.

6️⃣ Convert Array Slice to Array ⭐⭐

Often required in real projects.

✔ Resets indices to start from 0
✔ Interview favorite

7️⃣ Modifying Array Slices ❌

Array slices are read-only views.

❌ Not allowed:

✔ Convert to array first:

8️⃣ Slicing Using prefix and suffix ⭐

Safer and cleaner approach.

prefix(_:)

suffix(_:)

📌 These also return ArraySlice

9️⃣ Dropping Elements ⭐

✔ Useful for pipelines
✔ Returns ArraySlice

🔟 Array vs ArraySlice ⭐ (Interview)

1️⃣1️⃣ Common Mistakes ❌

❌ Assuming slice is an array
❌ Accessing slice with index 0
❌ Modifying slice directly
❌ Forgetting to convert slice to array

📌 Interview Questions & MCQs

Q1. Type of array[1...3]?

A) Array
B) Slice
C) ArraySlice
D) List

✅ Answer: C

Q2. Does ArraySlice copy data?

A) Yes
B) No

✅ Answer: B

Q3. How to convert ArraySlice to Array?

A) slice.toArray()
B) Array(slice)
C) slice.array()
D) convert(slice)

✅ Answer: B

Q4. Are ArraySlice indices reset?

A) Yes
B) No

✅ Answer: B

Q5. Which is safer for slicing?

A) Index ranges
B) prefix / suffix

✅ Answer: B

🔥 Real-Life Use Cases

✔ Pagination
✔ Processing subsets of data
✔ Performance-sensitive code
✔ Functional pipelines
✔ Interview coding questions

✅ Summary

• ArraySlice is a view, not a copy

• Created using ranges, prefix, suffix

• Keeps original indices

• Convert to Array when mutation is needed

• More memory-efficient than arrays

• Very important Swift interview topic