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29) More Pointers

Author: Jeyhun Abbasov

Interactive Learning

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More Pointers

In Go, function arguments are passed by value by default.

This means the function gets a copy of the value, not the original.

  Pass by Value                Pass by Pointer

  main:                        main:
  score = 10                   score = 10
     |                            |
     | copy                       | address
     v                            v
  double:                      double:
  n = 10  (separate copy)     n = &score (points to original)
  n = 20  (copy changed)      *n = 20   (original changed)
     |                            |
  main:                        main:
  score = 10 (unchanged)      score = 20 (modified!)

Pass by Value

func double(n int) {
    n = n * 2
}

score := 10
double(score)
fmt.Println(score) // 10

score is still 10. The function modified a copy, not the original.

Pass by Pointer

To modify the original variable, pass a pointer:

func double(n *int) {
    *n = *n * 2
}

score := 10
double(&score)
fmt.Println(score) // 20

score is now 20. The function received the address and modified the value at that address.

Notice two things:

• The parameter type is *int (pointer to int)
• The caller passes &score (address of score)

When to Use Pointers

↳ 1) When you need a function to modify the original value

↳ 2) When you want to avoid copying large data structures

Example Code

There are some pointer operations in main.go file.

But they are incomplete.

Fix the Code

Open main.go file and complete the code lines.

Then validate your code by running:

go run topic.go 29 validate

✅ If everything is ok, you should see:

OK!

Conclusion

Now you know how to pass pointers to functions in Go.

Continue to the next topic 👇

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