Mastering `for range` Loop: Iterating Collections in Go

In Go, iteration over collections such as arrays, slices, maps, or strings is commonly done using the for range loop. The for range loop provides a straightforward way to access both the index and the value of each element in the collection.

Examples of Using for range with Different Data Structures

1. Slices

package main

import (
	"fmt"
)

func main() {
	// Slice of integers
	numbers := []int{1, 2, 3, 4, 5}

	// Use `for range` to iterate over the slice
	for index, value := range numbers {
		fmt.Printf("Index: %d, Value: %d\n", index, value)
	}
}

2. Arrays

package main

import (
	"fmt"
)

func main() {
	// Array of strings
	fruits := [3]string{"Apple", "Banana", "Cherry"}

	// Use `for range` to iterate over the array
	for index, value := range fruits {
		fmt.Printf("Index: %d, Value: %s\n", index, value)
	}
}

3. Maps

package main

import (
	"fmt"
)

func main() {
	// Map of string keys to integer values
	scores := map[string]int{
		"Alice": 10,
		"Bob": 20,
		"Carol": 30,
	}

	// Use `for range` to iterate over the map
	for key, value := range scores {
		fmt.Printf("Key: %s, Value: %d\n", key, value)
	}
}

4. Strings

package main

import (
	"fmt"
)

func main() {
	// String
	s := "hello"

	// Use `for range` to iterate over the string (interpreted as runes)
	for index, runeValue := range s {
		fmt.Printf("Index: %d, Rune: %c\n", index, runeValue)
	}
}

Explanation of for range Loop

• Slices and Arrays: The for range loop returns both the index and the value of each element. If you only need the value, you can use the blank identifier _ to ignore the index.

for _, value := range numbers {
	fmt.Printf("Value: %d\n", value)
}

• Maps: The loop returns the key and the value for each entry in the map. If you only need the keys or values, use the blank identifier _ to ignore the other.

// Iteration over map keys only
for key := range scores {
	fmt.Printf("Key: %s\n", key)
}

• Strings: Iterates over each rune in the string, which is useful for handling Unicode characters. The loop returns the index of the rune and the rune itself.

Advanced Example with Structs

You might also want to iterate over a slice of structs. Here’s how you can do that:

package main

import (
	"fmt"
)

type Person struct {
	Name string
	Age  int
}

func main() {
	// Slice of Person structs
	people := []Person{
		{Name: "Alice", Age: 30},
		{Name: "Bob", Age: 25},
		{Name: "Carol", Age: 35},
	}

	// Use `for range` to iterate over the slice of structs
	for index, person := range people {
		fmt.Printf("Index: %d, Name: %s, Age: %d\n", index, person.Name, person.Age)
	}
}

By using the for range loop, you can easily iterate over different types of collections in Go. It provides a concise and readable syntax for accessing the elements, making your code clean and efficient.