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C++ Brain Teasers: Exercise Your Mind

Discussion: Will It Move?

Understand why moving from a const object in C++ still results in copying rather than moving. Learn about lvalues, rvalues, std::move, and how defaulted move constructors handle const members by using the copy constructor. This lesson deepens your grasp of object initialization nuances in C++.

We'll cover the following...

Run the code

Now, it’s time to execute the code and observe the output.

C++
#include <iostream>
struct Member
{
};
struct WillItMove
{
    WillItMove() = default;
    WillItMove(WillItMove &&) = default;
    const Member constMember_{};
};
int main()
{
    WillItMove objectWithConstMember;
    WillItMove moved{std::move(objectWithConstMember)};
    std::cout << "It moved!\n";
}

The WillItMove has a const member. We can’t move from a const object, so why could we still move from objectWithConstMember?

Understanding the output

In this puzzle, we first ...