How to Iterate Over Slice in Go: Simple Examples and Tips

In Go, you can iterate over a slice using a for loop with an index or a for range loop that gives both index and value. The for range loop is the most common and readable way to access each element in the slice.

Syntax

There are two main ways to loop over a slice in Go:

• Using a classic for loop: You use an index to access each element.
• Using a for range loop: This gives you both the index and the value directly.

Example syntax:

for i := 0; i < len(slice); i++ {
    value := slice[i]
    // use value
}

for i, value := range slice {
    // use i and value
}

go

for i := 0; i < len(slice); i++ {
    value := slice[i]
    // use value
}

for i, value := range slice {
    // use i and value
}

Example

This example shows how to print all elements of a slice using both the classic for loop and the for range loop.

go

package main

import "fmt"

func main() {
    fruits := []string{"apple", "banana", "cherry"}

    fmt.Println("Using classic for loop:")
    for i := 0; i < len(fruits); i++ {
        fmt.Println(i, fruits[i])
    }

    fmt.Println("\nUsing for range loop:")
    for i, fruit := range fruits {
        fmt.Println(i, fruit)
    }
}

Output

Using classic for loop:
0 apple
1 banana
2 cherry

Using for range loop:
0 apple
1 banana
2 cherry

Common Pitfalls

One common mistake is to use the for range loop but accidentally capture the loop variable's address inside a closure, which leads to unexpected results.

Also, forgetting that the range loop returns a copy of the element, not a reference, can cause bugs when modifying elements.

go

package main

import "fmt"

func main() {
    nums := []int{1, 2, 3}
    var ptrs []*int

    // Wrong: appending address of loop variable (same variable reused)
    for _, n := range nums {
        ptrs = append(ptrs, &n)
    }

    for _, p := range ptrs {
        fmt.Println(*p) // prints 3, 3, 3 instead of 1, 2, 3
    }

    // Correct: use index to get address of slice element
    ptrs = nil
    for i := range nums {
        ptrs = append(ptrs, &nums[i])
    }

    for _, p := range ptrs {
        fmt.Println(*p) // prints 1, 2, 3
    }
}

Output

3
3
3
1
2
3

Quick Reference

Tips for iterating over slices in Go:

• Use for range for clean and readable code.
• Remember range returns a copy of the element, not a pointer.
• Use classic for loop if you need to modify elements by index.
• Be careful when capturing loop variables inside closures.

Key Takeaways

Use for range loops to iterate over slices easily and readably.

Range returns copies of elements; use index if you need references.

Avoid capturing loop variables' addresses directly in closures.

Classic for loops give full control with indexes for modification.

Remember slice length with len(slice) when using classic loops.