Re: [boost] [operators] The future of Boost.Operators

Subject: Re: [boost] [operators] The future of Boost.Operators
From: Daryle Walker (darylew_at_[hidden])
Date: 2013-04-25 07:19:13

-----Original Message----- 
From: Daniel Frey
Sent: Monday, April 22, 2013 3:43 PM

> Hello,
>
> for a long time there hasn't been any significant update of 
> Boost.Operators and I had an easy job being its maintainer for the past 
> 10+ years. I guess that will change soon. :)

> I would like to discuss the future of Boost.Operators, as several issues 
> and options have piled up in the past. Here are some points to take into 
> account:

> 1) Support for rvalue references to generate fewer temporaries. (where 
> available)
> 2) Support for noexcept. (where available)
> 3) Support for constexpr if this is applicable at all. I haven't found the 
> time to properly research it yet.

I've discussed this somewhere, but this library and constexpr are 
incompatible.  The dependency between operator?? and operator??= is 
backwards to what constexpr needs.

    template < typename T >
    class my_complex {
        T  d[2];
    public:
        my_complex( r = T{}, I = T{} ) : d{r, i} {}
        //...
    };

    template < typename T >
    inline constexpr
    my_complex<T>  operator/( my_complex<T> x, T y )
    { return my_complex{x.real() / y, x.imag() / y}; }

    template < typename T >
    inline
    my_complex<T> &  operator/=( my_complex<T> &x, T y )
    { return x = x / y; }

You can compose the regular version of an operator in a constexpr way if you 
have the right initialization.  But the compound-assignment operators are 
inherently mutating, so they can never be constexpr.  Defining the regular 
versions in terms of the compound-assignment ones bars them from being 
constexpr.  You can reverse the dependencies to save code.

> 4) Allow dedicated commutative and non-commutative versions for several 
> operators, leading to fewer temporaries for commutative versions in 
> several cases.
> 5) Remove work-arounds for ancient compilers, general cleanup.
[TRUNCATE]

Daryle W.