Re: [Boost-users] [fusion] memory layout of fusion::vector vs boost::tuple/boost::array

On 10/9/2010 2:44 AM, alfC wrote:

On Oct 6, 5:33 pm, Joel de Guzman wrote:

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On 10/7/2010 3:53 AM, alfC wrote:

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Hi,

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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? (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.

No it is not. 1) It is not documented 2) It is not a POD 3) Anything with a reinterpret_cast is not guaranteed to work (you can only rely on reinterpret_cast only when casting back from a lost type e.g. through type erasure). Disregarding any of that is playing with fire. Regards, -- Joel de Guzman http://www.boostpro.com http://spirit.sf.net