📂 Go Arrays, Slices & Maps – The Core Data Containers in Golang

🧲 Introduction – Why Learn Arrays, Slices & Maps in Go?

In Go, arrays, slices, and maps are the foundation of data structures. They allow you to organize data sequentially (arrays/slices) or in key-value pairs (maps). Go provides simple syntax, built-in safety, and efficient memory handling for these containers.

🎯 In this guide, you’ll learn:

• How to declare and manipulate fixed-size arrays
• How slices offer dynamic, resizable collections
• How maps store key-value pairs efficiently
• How to pass arrays/slices to functions
• How multidimensional arrays work in Go

---

📘 Topics Covered

🔹 Topic	📖 Description
🧱 Go Arrays	Fixed-size collections of same-type elements
🧊 Go Multidimensional Arrays	Arrays of arrays—used for matrices or grids
🧪 Go Passing Arrays to Functions	Learn how arrays behave when passed by value or reference
📦 Go Slices	Dynamic, resizable views over arrays
🗺️ Go Maps	Key-value pairs with fast lookup and insertion

---

🧱 Go – Arrays

🔹 Declare and Access

var nums [3]int = [3]int{10, 20, 30}
fmt.Println(nums[1]) // 20

Or shorthand:

nums := [...]int{1, 2, 3}

🔍 Key Properties:

• Fixed length
• Elements initialized to zero values
• Length set at compile time

---

🧊 Go – Multidimensional Arrays

matrix := [2][3]int{
    {1, 2, 3},
    {4, 5, 6},
}

fmt.Println(matrix[1][2]) // 6

🧠 Used in:

• Grid-based games
• Matrix math
• Tabular data

---

🧪 Go – Passing Arrays to Functions

Arrays are passed by value in Go (a full copy):

func update(arr [3]int) {
    arr[0] = 99
}

func main() {
    a := [3]int{1, 2, 3}
    update(a)
    fmt.Println(a[0]) // 1 (unchanged)
}

✅ Use slices or pointers for memory-efficient mutation.

---

📦 Go – Slices

🔹 Declare and Use

nums := []int{10, 20, 30}
fmt.Println(nums[0]) // 10

🔁 Slice from an array

arr := [5]int{1, 2, 3, 4, 5}
slice := arr[1:4]
fmt.Println(slice) // [2 3 4]

✅ Built-in Functions

Function	Description
len()	Length of slice
cap()	Capacity from starting index
append()	Add elements dynamically
copy()	Copy elements from one slice to another

nums := []int{1, 2}
nums = append(nums, 3, 4) // [1 2 3 4]

✅ Slices are passed by reference-like behavior—backed by arrays.

---

🗺️ Go – Maps

🔹 Declare and Use

ages := map[string]int{
    "Alice": 25,
    "Bob":   30,
}

fmt.Println(ages["Alice"]) // 25

🧠 Add / Update / Delete

ages["Eve"] = 22         // Add
delete(ages, "Bob")      // Delete
val, exists := ages["Tom"]

✅ Maps return two values on access: value and bool indicating existence.

---

📌 Summary – Recap & Next Steps

Go’s array, slice, and map types provide lightweight yet powerful data containers. Slices and maps are used most commonly in real-world Go development thanks to their dynamic and flexible nature.

🔍 Key Takeaways:

• Arrays are fixed-size, zero-initialized collections
• Slices are dynamic, built on arrays, and allow resizing
• Maps store key-value pairs with fast access
• Arrays are passed by value; slices behave more like references
• Use append, copy, and delete for data manipulation

⚙️ Real-World Use Cases:

• Slices for dynamic lists (e.g., user inputs, query results)
• Maps for fast lookups (e.g., cache, dictionary)
• Arrays for performance-critical static datasets

---

❓ Frequently Asked Questions

❓ What’s the default value of an array in Go?
✅ All elements are initialized to their zero value (e.g., 0 for int, "" for string).

---

❓ Can I resize an array in Go?
✅ ❌ No. Arrays are fixed size. Use slices for resizing.

---

❓ Do slices copy the underlying array?
✅ No. Slices share the underlying array, so changes reflect across copies unless explicitly cloned.

---

❓ Are maps ordered in Go?
✅ ❌ No. Go maps are unordered. Iteration order is not guaranteed.

---

❓ How do I check if a map key exists?
✅ Use:

val, ok := myMap["key"]
if ok {
    fmt.Println("Exists:", val)
}

---

Share Now :