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Subject: Re: [boost] [offtopic] C++11 useful trick
From: Dave Abrahams (dave_at_[hidden])
Date: 2012-07-28 22:10:34

on Wed Jul 04 2012, Eric Niebler <> wrote:

> He's using a variant of the variadic tuple trick. He wants to find the
> Nth element in a parameter pack. So he puts all the elements in a
> tuple-like thingy (select_impl) which holds individual elements, each
> in its own base class (select_base). But only the Nth base actually
> holds onto its argument. (See the partial specialization of
> select_base.) His solution instantiates O(N) instances of select_base,
> but gets you the Nth element in O(1). Fiendishly clever.

That explanation doesn't match what I'm seeing in his latest attachment
(, which doesn't
require storing anything. Which is pretty cool!

Dave Abrahams
BoostPro Computing                  Software Development        Training             Clang/LLVM/EDG Compilers  C++  Boost

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