Re: [Boost-users] Getting metadata of class

Subject: Re: [Boost-users] Getting metadata of class
From: OvermindDL1 (overminddl1_at_[hidden])
Date: 2009-12-11 18:56:39

On Fri, Dec 11, 2009 at 10:45 AM, Alex Vinokur
<alexvn_at_[hidden]> wrote:
> Hi,
>
> Does Boost contain any features to get metadata of classes?
>
> For instance,
>
> Let Foo be some class
>
> class Foo
> {
>  int   m_var1;
> Â long* Â m_var2]
>  char   m_var3[100];
>  dooble  m_var4;
> };
>
> I would like to get the following info (as vector, file, etc) of its
> members:
>
> {" m_var1", "int", sizeof (m_var1), offset of (m_var1) },
> {" m_var2", "long", "Pointer", sizeof (m_var2), sizeof (base-variable, i.e.,
> long), offset of (m_var2 },
> {" m_var3, "char", "array", sizeof (m_var3), sizeof (base-variable, i.e.,
> char), offset of (m_var3 },
> {" m_var4", "double", sizeof (m_var4), offset of (m_var4) },
>
> That info I would like to get as a result of some feature (function, ...)
> applied to class Foo, not to each member of Foo.

C++ is not introspective nor reflective, hence there is no way to do
that according to the language spec.  However, you can use Fusion to
'convert' your stucts to a fusion map or vector (depending on if you
need names or not) and work on it at compile time, and there is an
introspective/reflective library in the sandbox if you do not mind
adding things directly to your structs, it has more power for asking
information about things instead of just operating on it like with
Fusion, but you cannot operate on the things like you can with Fusion,
depends on what you are needing to do...  There are a few external
things like gcc-xml that you can parse the info from as well.

All in all, no easy way to do this.  Would be nice if C++ had this
ability built in (no real reason why it cannot for compile-time work),
but meh...