Delegating deleter

delegating_deleter.h

/////////////////////////////////////////////
// parser.h
#include <memory>

template<class T>
struct delegating_delete {
    inline void operator() (T *p) const noexcept { do_delete(p); }
};

namespace parser {
    class Parser {
    public:
        // ...
    private:
        class Impl;

        friend void do_delete(Impl *p) noexcept;

        std::unique_ptr<Impl, delegating_delete<Impl>> impl_; // PIMPL
    };
}

/////////////////////////////////////////////
// parser.cpp
#include "parser.h"

namespace parser {
    class Parser::Impl { ... };

    void do_delete(Parser::Impl *p) noexcept { delete p; }

    // Parser implementation...
}