Re: [boost] [generic programming] header file for general "default" operations for C++ classes

Subject: Re: [boost] [generic programming] header file for general "default" operations for C++ classes
From: Walt Karas (wkaras_at_[hidden])
Date: 2016-05-04 15:45:47

Andrey Semashev <andrey.semashev <at> gmail.com> writes:

> 
> On Wednesday, 4 May 2016 17:01:49 MSK Walt Karas wrote:
> > In C++, a default assignment operator is generated for a class if all of its
> > components (data members and base classes) have an assignment operator. 
> > There are plans in C++17 to do something similar for comparison operators. 
> > This header, in
> > https://github.com/wkaras/C-plus-plus-library-default-operators ,
> > facilitates that, more generally, if there is an operation on all the
> > components of a class, a single macro invocation can provide this operation
> > on the class as well.  A big drawback is that it's very intrusive into the
> > class definition.  Each class component must be defined using a macro,
> > COMPOSITE_OP_MBR_T(int) i; for examle.  The class will in truth be a
> > template, with the template parameter being defaulted for normal usage.  I
> > don't know which, if any, existing Boot library this header would belong
> > in.
> 
> I think, Boost.Fusion already provides this for all adapted types.
> 
> http://www.boost.org/doc/libs/1_60_0/libs/fusion/doc/html/fusion/sequence/
> operator/comparison.html

Yes, but there is not full overlap of the capabilities.  Fusion doesn't seem
to provide a way to define a class with access control, base classes, and
member functions as a sequence.  I'm assuming BOOST_FUSION_DEFINE_STRUCT has
no runtime overhead, although I could not find and explicit statement to
that effect.