C++ Brain Teasers: Exercise Your Mind/

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Discussion: Will It Move?

Discussion: Will It Move?

Execute the code to understand the output and gain insights into move constructors.

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 initialize WillItMove objectWithConstMember;. Then, on line 17, we initialize a new WillItMove moved{std::move(objectWithConstMember)};. Since WillItMove has no copy constructor, the only alternative to initialize moved is the move constructor. But how can the move constructor perform a move operation from the const Member constMember?

The move constructor

Let’s start digging from the outside in.

First, what does std::move(objectWithConstMember) do? The ...

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