Re: [Boost-users] multi-inheritance from elements of mpl::vector?==> inherit_scattered ( for Barton & Nackmann trick)

From: David Abrahams (dave_at_[hidden])
Date: 2005-10-27 10:05:43

<Oliver.Kowalke_at_[hidden]> writes:

>>>no reply - so I found a solution by myself (used for the Barton &
>>> Nackmann trick)!
>>> template< typename D >
>>> struct F
>>> {
>>> 	std::string f()
>>> 	{ return static_cast< D & >( * this).str_; }
>>> };
>>>
>>> template< typename D >
>>> struct G
>>> {
>>> 	std::string g()
>>> 	{ return static_cast< D & >( * this).str_; }
>>> };
>>
>>That's not the B&N trick; it's simple CRTP.
>>The B&N trick is the one where you stick a friend function that
>>applies to the derived class in the base class.  See the operators
>>library for reference.
>
> Sorry - in your book (C++ Template Metaprogramming, page 205) I can
> read:
> "The technique of using a static_cast with CRTP to reach the derived
> object is sometimes called the "Barton and Nackmann trick" ...".
> Is this wrong?

No, I guess you're right; if you read the Wikipedia definition I
cited, you'll see:

    Today the Barton-Nackman trick has become synonymous with
    "curiously recurring templates" (a term due to Coplien [4], but
    which Barton and Nackman popularized), in which a base class
    template is instantiated with a derived class type as its template
    parameter...

Sorry about the noise.
-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com