Patterns for resetting objects to initial state

Question

Suppose I have an object with a member that is expensive to construct, and the need for a reset() function that resets it to its initial state:

struct Example
{
    // option 1: efficient, but need to duplicate initialization logic of reset() 
    Example(int param) : expensive_member_(param), param_(param)
    {
    }
    /* option 2: less code, but initializes expensive_member_ twice
    Example(int param) : param_(param)
    { 
        reset();
    }*/

    void reset()
    {
         expensive_member_ = ClassWithExpensiveConstructor(param_);
    }

    ClassWithExpensiveConstructor expensive_member_;
    int param_;
}

Is there a better way of/pattern for efficiently resetting the object to its initial state without duplicating the initialization logic in the initializer list and the reset function?

edit: If there is no generic way of achieving what I want, that is also an acceptable outcome of this question!

Answer 1

You can make your ExpensiveMember a pointer, in such case your option 2 will not call ExpensiveMember constructor in Example constructor unless you explicitly call it:

struct Example
{
    Example(int param) : expensive_member_(), param_(param)
    { 
         reset();
    }

    ~Example() {
         delete expensive_member_;   // better use unique_ptr etc
    }

    // Also a copy constructor and assignment operator 
    // are needed to avoid memory problems such as double-delete.
    // Also, better use unique_ptr etc.
    // This answer does not use unique_ptr just to make the main idea more clear.

    void reset()
    {
         delete expensive_member_;   // better use unique_ptr etc
         expensive_member_ = new ClassWithExpensiveConstructor(param_);
    }

    ClassWithExpensiveConstructor* expensive_member_;  // better use unique_ptr etc
    int param_;
}