Prevent passing temporary for const ref parameter

Question

I have a function:

void AddImage(const Image &im);

This function does not need image to be modifiable, but it stores the image a const reference to be used later. Thus, this function should not allow temporaries. Without any precaution the following works:

Image GetImage();

...

AddImage(GetImage());

Is there a way to prevent this function call?

Answer 1

There are couple of mechanisms that prevent passing temporary to a const ref parameter.

1. Delete the overload with r-value parameter: void AddImage(const Image &&) = delete;

2. Use const pointer: void AddImage(const Image*) . This method will work pre-C++11

3. Use reference wrapper: void AddImage(std::reference_wrapper<const Image>)

First method should be preferred when using C++11 supporting compiler. It makes the intention clear. Second method requires a runtime check of nullptr and does not convey the idea that the image cannot be null. Third method works and makes the intention clear, however, it is too explicit.