Using unique_ptr to control a file descriptor

Question

In theory, I should be able to use a custom pointer type and deleter in order to have unique_ptr manage an object that is not a pointer. I tried the following c

Answer 1

The type exposed by the Deleter::pointer must satisfy the NullablePointer requirements. Chief among them, this expression must be legal: Deleter::pointer p = nullptr;. Of course, nullptr is pretty much defined by the fact that it cannot be implicitly converted to a number, thus this doesn't work.

You'll have to use a type which can be implicitly constructed with std::nullptr_t. Something like this:

struct file_desc
{
  file_desc(int fd) : _desc(fd) {}
  file_desc(std::nullptr_t) : _desc(-1) {}

  operator int() {return _desc;}

  bool operator ==(const file_desc &other) const {return _desc == other._desc;}
  bool operator !=(const file_desc &other) const {return _desc != other._desc;}
  bool operator ==(std::nullptr_t) const {return _desc == -1;}
  bool operator !=(std::nullptr_t) const {return _desc != -1;}

  int _desc;
};

You can use that as the Deleter::pointer type.