无法保持我的健康

Question

I have a Node class defined like this (this is a minimal version):

class Node {
    private:
        std::vector <const Node*> leaves;

     public:
        Node* getLeaf(int i);
}

In other words, I want getLeaf to return a pointer to an element of the vector "leaves"

I tried defining getLeaf like so

Node* Node::getLeaf(int i){
    return leaves[i];
}

Ok, so I know I'm screwing the constness up. I've tried variations of const modifiers in my function declarations / definitions to no luck. Someone please help :)

Answer 1

const is a promise to not change.

You declare a vector of pointers to const nodes. That's a promise to not change any Node via these pointers.

The getLeaf function can't very well then return a pointer to non- const node, because then the caller can do anything with the node.

So you have to make either the same promise both places, or don't make any such promise.

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Another matter is whether getLeaf itself should be const (it probably should, it makes sense to let it promise not to change the object), and a second other matter is whether get makes sense as a prefix in C++ (usually not, it's just needless verbosity, while in Java there are tools that can make good use of such of prefix), I'd just call it node .