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Subject: Re: [boost] [type_at] Variadic template utility
From: tymofey (tymofey_at_[hidden])
Date: 2011-05-26 07:41:57


>Larry Evans <cppljevans_at_[hidden]> > On 05/26/11 04:47, tymofey wrote: > >> Robert Jones <robertgbjones_at_[hidden]> > >> On Thu, May 26, 2011 at 8:34 AM, tymofey <tymofey_at_[hidden]> wrote: > >> > >>> While experimenting with varidic templates of the upcoming standard i > >>> discovered that quite often one would need to extract a type from parameter > >>> pack at specified position. > [snip] > >> Forgive me if I'm missing the point, but isn't this essentially Boost.MPL's > >> 'at' metafunction? > >> > >> - Rob. > > > > It is, but without the need to drag in mpl::vector with the limitations it imposes. > > > Could you please describe those limitations, other than the one for > maximum arity, which, IIUC, is modifiable by redefining the macro: > > BOOST_MPL_LIMIT_VECTOR_SIZE > > ? Also, IIUC, one reason for using the macro, and the preprocessor, > is to speed compile time by reducing the number of template > instantiations. Thus, maybe one advantage of mpl::at vs your type_at > is compile time. You might check that somehow. > > -regards, > Larry The size of the vector is the only limitation i'm know of. And I wasn't aware that one can change it thus making my proposal pretty usless. Thanks for the info.


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