Can You Reassign Pointers Within Golang Struct Pointer Methods?

Can Pointers in Struct Pointer Methods Be Reassigned in Golang?

In Golang, struct pointer methods allow modifications to be made to the receiver struct without the need to explicitly pass a pointer. However, many developers encounter difficulty when attempting to reassign the primary pointer within a struct pointer method.

One particular scenario involves the AVL tree, where the tree.rotateLeftToRoot() method does not update the tree pointer outside the scope of the function. This has led to the question of能否在函数作用域外重新分配结构指针方法中的指针，或是否不鼓励这样做？

Understanding Pointers and Values

Pointers in Golang represent memory addresses, while other data types (such as integers) represent their own values. When modifying variables of type *T (where T is any data type), it is necessary to pass a pointer to that variable (**T). This allows for modifying the pointed object (the value at the memory address) rather than just the copy of the pointer.

Limitations of Receiver Types

In the case of struct pointer methods, the receiver cannot be a pointer of a pointer (**T). This means that the pointer within a struct pointer method cannot be directly reassigned.

Solutions to Reassignment

There are two possible solutions:

1. Create a non-pointer function that takes **T as input and modifies the pointed value.
2. Return the *T pointer from the method and assign it to the original pointer variable in the caller function.

Example Implementations

Non-Pointer Function:

func rotateLeftToRoot(ptree **AvlTree) {
    tree := *ptree
    if tree == nil {
        return
    }
    prevLeft := tree.left
    if prevLeft != nil {
        tree.left = prevLeft.right
        prevLeft.right = tree
        tree = prevLeft
    }
    *ptree = tree
}

Method with Returned Pointer:

func (tree *AvlTree) rotateLeftToRoot() *AvlTree {
    if tree == nil {
        return nil
    }
    prevLeft := tree.left
    if prevLeft != nil {
        tree.left = prevLeft.right
        prevLeft.right = tree
        tree = prevLeft
    }
    return tree
}

In either case, the desired effect can be achieved. However, it is important to note that returning the pointer from a method is common practice, especially when modifications to the underlying data structure are made.

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