On Oct 6, 5:33 pm, Joel de Guzman <j...@boost-consulting.com> wrote:
On 10/7/2010 3:53 AM, alfC wrote:
Hi,
I am trying to convert a boost::array into a fusion::vector. reinterpreting the memory from boost::array. It works for tuples but not fusion::vector, why is that. Is there a way to make it work? ( I was hoping that the memory layout is the same to make conversion from one to the other very easy.)
Don't do that. It will *never* be guaranteed to work even if it works now. The memory layout of fusion::vector is an internal implementation detail and can change anytime.
The question is: is it guaranteed for boost::tuples<double, double, ... >? (it seems so, just by the PODness of tuples of PODs in its stated design.) If so, then it is a *feature* of boost::tuple. Fusion, which is supposed to be an extension of boost::tuple (or at least that was my understanding), lost such feature that I could exploit. The situation is the following: quantity<U,T> because it claims that has no runtime cost, this is like saying that it can be interpreted as its underlying type T (e.g. double). All numerical routines that I am using take fixed arrays of double or basically boost::arrays. The analogy is perfect if I use tuples because I can reinterpret them as arrays back *and* forth without copying anything or adding any additional code. Since I can't do this with fusion::vector then I will have to use boost::tuples. This will be a pain in it self because then I will have to manually code MPL to tuples generation and loose the nice fusion::transforms. It seem I am out of luck, and just fallen in a crack between tuples and fusion. There is second possibility that is that I got the boost::fusion theory totally wrong in the first place. Thanks so much for your help, Alfredo.
Regards, -- Joel de Guzmanhttp://www.boostpro.comhttp://spirit.sf.net
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