When I first started learning Go, I thought I was doing everything right—until I ran into a weird bug about golang range loop reference. I was iterating over a list of Book structs (of course, I can't share the real structs and code used here... all here are for turorial purpose), taking the pointer of each one, and storing them into a slice. But at the end of the loop, all the pointers pointed to... the same book?! 🤯

Let’s walk through this classic Go beginner mistake together — and fix it the right way.

📚 The Use Case: A Slice of Books in a Library

Suppose we have a list of books, and we want to collect pointers to each one so we can modify them later.

Here’s the code I thought would work:

for _, book := range books {
    bookPointers = append(bookPointers, &book) // Oops...
}

But when I printed out the pointers, they all pointed to the last book in the list. This bug stumped me for a while until I understood one critical Go behavior.

The File Structure To Run The Code

learning-golang/
├── 01-loop-reference-pitfall/
│   ├── main.go
│   └── README.md
├── Makefile
├── bin/
└── go.mod

This is the complete buggy code:

package main

import (
    "fmt"
)

type Book struct {
    Title  string
    Author string
}

func main() {
    originalBooks := []Book{
        {"Go in Action", "William Kennedy"},
        {"The Go Programming Language", "Alan Donovan"},
        {"Introducing Go", "Caleb Doxsey"},
    }

    fmt.Println("❌ Buggy Version:")
    var buggyPointers []*Book
    for _, book := range originalBooks {
        buggyPointers = append(buggyPointers, &book)
    }
    for _, bp := range buggyPointers {
        fmt.Printf("Title: %-30s | Address: %p\n", bp.Title, bp)
    }
}

The Makefile:

# Usage:
#   make run DIR=01-loop-reference-pitfall
#   make build DIR=01-loop-reference-pitfall
#   make clean

GO=go

run:
    @echo "👉 Running $(DIR)/main.go..."
    cd $(DIR) && $(GO) run main.go

build:
    @echo "🔧 Building binary from $(DIR)/main.go..."
    cd $(DIR) && $(GO) build -o ../bin/$(notdir $(DIR))

clean:
    @echo "🧹 Cleaning up built binaries..."
    rm -rf bin/

Build and Run The Code

❯ go mod init github.com/geekcoding101/learning-golang
❯ make run DIR=01-loop-reference-pitfall

As you see, the Address didn't change at all!

🐛 The Problem: Reuses the Loop Variable in Golang Range Loop Reference

In Go, when you do:

for _, book := range books

This means every pointer in the slice is just pointing to the same memory location, which at the end holds the value of the last book.

✅ The Fix: Indexing Directly

The correct way is to use an index:

fmt.Println("\n✅ Fixed Version:")
var fixedPointers []*Book
for i := range originalBooks {
    fixedPointers = append(fixedPointers, &originalBooks[i])
}
for _, bp := range fixedPointers {
    fmt.Printf("Title: %-30s | Address: %p\n", bp.Title, bp)
}

Now, each pointer actually refers to the corresponding element in the original slice. Problem solved!

💻 Real Code Example on GitHub

I've documented this bug and fix in my GitHub repository:

👉 github.com/geekcoding101/learning-golang

Here's what you’ll find:

• The buggy version (with all pointers pointing to the same book)

• The fixed version (each pointer is correct)

• A Makefile to help you run and build each learning topic

✍️ Follow My Golang Tutorials

I’ll continue sharing these hands-on lessons as I deepen my understanding of Go.

Check out my blog 👉 www.geekcoding101.com — where I share practical posts, breakdowns, and real-world insights from my coding journey.

📌 Quick Hashtag

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