Re: [boost] [fusion] fusion sequence of non-copy-constructible types

From: oliver (oliver.mueller_at_[hidden])
Date: 2008-07-07 10:30:18

Joel de Guzman <joel <at> boost-consulting.com> writes:

> 
> Hmm... well...
> a) How do you put a noncopyable object in a container?
> b) How do you copy a container with noncopyable elements?
> 

what i really wanna do is not to name the objects i put i the 
fusion vector.
they should be constructed in place and only be accessed through the 
fusion vector.
should look something like this:

typedef boost::fusion::vector<JobA, JobB, JobC> tJobs;
struct System
{
  System(Da& da) : fJobs(JobA(da), JobB(da, 2), JobC(da, 3))
  {}
private:
  tJobs  fJobs;
};

there are several operations that need to include all jobs - non has to be 
left out - and to avoid repetitive coding, it would be nicer to only operate 
on fJobs.

> Fusion vector is based on stl vector. Even stl vector requires copy
> constructible types.
> 
> One possibility is to store your object in a smart pointer or
> wrap it in a reference wrapper. Then, the smart pointer and
> reference wrapper can be stored in the fusion container.
> 
but doesn't it make a difference that the stl sequences are 
runtime-extensible?
you always get an empty sequence and add to it at runtime. 
with fusion::vector, i know exactly in advance how many objects i need to 
create (i mean at compile time), and i have to explicitly call 
the constructor in the
initialization list. from this point of view i thought it rather 
behaves like the initialization of an array.