Can a Go Struct Pointer Method Reassign its Receiver Pointer to a Different Instance?

Can the Pointer in a Struct Pointer Method Be Reassigned to Another Instance?

When working with pointers in Go struct methods, reassigning the primary pointer to another instance can be challenging. This is different from reassigning a pointer to a regular Go struct.

Background: Pointer Values

In Go, pointers are values that store the memory address of another variable. When modifying a pointer value, you are actually modifying the pointed variable, not the pointer itself.

Pointer Methods and Receiver Base Type

In Go, struct pointer methods must have a receiver base type of T, where T is the type of the struct. This means that the receiver cannot be a pointer to a pointer to T.

Options for Reassigning Pointer

1. Pass Pointer to Pointer Function:

This involves writing a non-method function that takes a pointer to a pointer to the struct. Inside the function, you can then modify the pointed pointer.

func rotateLeftToRoot(ptree **AvlTree) {
    // Pointer to the pointer to the AvlTree
    tree := *ptree

    // Update pointer to the new root
    *ptree = tree
}

2. Return the Updated Pointer:

This involves returning the updated pointer from the method, and then assigning it to the desired variable in the calling code.

func (tree *AvlTree) rotateLeftToRoot() *AvlTree {
    // Update pointer to the new root
    prevLeft := tree.left
    if prevLeft != nil {
        tree.left = prevLeft.right
        prevLeft.right = tree
        tree = prevLeft
    }
    return tree
}

// Usage:
tree = tree.rotateLeftToRoot()

Returning Trees in General:

Returning trees from methods is not uncommon in Go, particularly in data structure manipulation. Just like the append() function in the Go standard library returns the updated slice, it may be necessary to return a modified tree pointer to achieve the desired tree update.

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