How to static_cast std::unique_ptr

01 Jan 2013 | One-minute read

I’ve been writing a lot of code using std::unique_ptr, new in standard library changes for C++11. One of the thing the library doesn’t provide is a way to cast std::unique_ptr, for example, from a base type to a derived type.

I wrote a couple of helper functions that is probably useful for someone else. They obey the basic rule for std::unique_ptr, that one object owns the memory. They also work well with the auto keyword, and so can save you a lot of typing

template<typename D, typename B>
std::unique_ptr<D> static_cast_ptr(std::unique_ptr<B>& base)
{
    return std::unique_ptr<D>(static_cast<D*>(base.release()));
}
  
template<typename D, typename B>
std::unique_ptr<D> static_cast_ptr(std::unique_ptr<B>&& base)
{
    return std::unique_ptr<D>(static_cast<D*>(base.release()));
}

You can see the code in action on ideone.com.

Note As noted in a prior comment section, this code is not safe to temporarily cast the pointer.