koie blog : boost::scoped_ptr/boost::checked

boost::scoped_ptrはデストラクタが定義されていないとエラーになるという話がなかなかわかったが、人から説明をうけてやっとわかった。

http://twitter.com/SubaruG/status/14747212751
http://twitter.com/SubaruG/status/14747268037
http://twitter.com/SubaruG/status/14747325492

=== main.cc ===
     1  #include "hoge.h"
     2  int
     3  main()
     4  {
     5      hoge h;
     6  }
=== hoge.h ===
     1  #include <boost/scoped_ptr.hpp>
     2  struct hoge
     3  {
     4      hoge();
     5      ~hoge() {} //もしデストラクタをユーザ定義しないとすると、コンパイラがデフォルトでこんなのを生成する
     6   private:
     7      class impl;
     8      boost::scoped_ptr<impl> pimpl_;
     9  };
=== impl.cc ===
     1  #include "hoge.h"
     2  #include <iostream>
     3  struct hoge::impl
     4  {
     5      impl() { std::cout << "impl+" << std::endl; }
     6      ~impl() { std::cout << "impl-" << std::endl; }
     7  };
     8  hoge::hoge() : pimpl_(new hoge::impl) {}

% c++ -I/usr/local/include -c main.cc
/usr/local/include/boost/checked_delete.hpp: In function 'void boost::checked_delete(T*) [with T = hoge::impl]':
/usr/local/include/boost/smart_ptr/scoped_ptr.hpp:80:   instantiated from 'boost::scoped_ptr::~scoped_ptr() [with T = hoge::impl]'
hoge.h:5:   instantiated from here
/usr/local/include/boost/checked_delete.hpp:32: error: invalid application of 'sizeof' to incomplete type 'hoge::impl'
/usr/local/include/boost/checked_delete.hpp:32: error: creating array with negative size ('-0x00000000000000001')
/usr/local/include/boost/checked_delete.hpp:33: error: invalid application of 'sizeof' to incomplete type 'hoge::impl'
/usr/local/include/boost/checked_delete.hpp:33: error: creating array with negative size ('-0x00000000000000001')
/usr/local/include/boost/checked_delete.hpp:34: warning: possible problem detected in invocation of delete operator:
/usr/local/include/boost/checked_delete.hpp:29: warning: 'x' has incomplete type
hoge.h:7: warning: forward declaration of 'struct hoge::impl'
/usr/local/include/boost/checked_delete.hpp:34: note: neither the destructor nor the class-specific operator delete will be called, even if they are declared when the class is defined.
*** Error code 1

なぜメンバ変数 piml_ の実体化のところで、その外にあるクラスのデストラクタの有無が影響してくるのかだが、