How to Create True Copies of Interface Values in Go When Dealing with Pointer References?

Copy Versus Reference in Interface Values

In Go, you may encounter scenarios where you need to create copies of interface values to maintain distinct state. When copying interface values that hold pointer references, it's crucial to consider the implications. This article explores how to handle such scenarios and provides techniques to create true copies.

The Problem: Sharing Values Through Pointer References

In the given example, user1 references an Admin struct via a pointer. This means that when you assign user1 to user2, you are essentially making user2 point to the same underlying Admin struct. Any modifications made through either user1 or user2 will affect the original struct.

Solution 1: Explicitly Copying the Underlying Struct

One approach to create distinct copies is to type assert the value in user1, copy the underlying Admin struct, and wrap its address in a new User value:

var user2 User
padmin := user1.(*Admin) // Obtain *Admin pointer
admin2 := *padmin        // Make a copy of the Admin struct
user2 = &admin2          // Wrap its address in another User

Solution 2: Using Reflection

For a more generic solution, you can leverage Go's reflection capabilities to retrieve the underlying type, dynamically create a new value of that type, and wrap it in a new User value:

if reflect.TypeOf(user1).Kind() == reflect.Ptr {
    // Pointer:
    user3 = reflect.New(reflect.ValueOf(user1).Elem().Type()).Interface().(User)
} else {
    // Not pointer:
    user3 = reflect.New(reflect.TypeOf(user1)).Elem().Interface().(User)
}

By using reflection, you can handle cases where the value in user1 is not a pointer.

Conclusion

In cases where interface values need to be copied and remain distinct, it's important to carefully consider the underlying type and use appropriate techniques such as explicit copy or reflection to create true copies. These approaches allow you to modify one copy without affecting the original.

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