Re: [boost] New library proposal: Autodiff

Subject: Re: [boost] New library proposal: Autodiff
From: Peter Dimov (lists_at_[hidden])
Date: 2018-12-20 19:48:48

Matt Pulver wrote:

> For example, the following will not compile with pre-17 compilers if 
> `constexpr` is dropped:
>
> template<typename RealType,size_t Order>
> constexpr size_t dimension<RealType,Order>::depth()
> {
>     if constexpr (is_dimension<RealType>::value)
>         return 1 + RealType::depth();
>     else
>         return 1;
> }

This specific case isn't hard to support either, although whether you would 
want to invest the effort is up to you.

template<typename RealType,size_t Order>
constexpr size_t dimension<RealType,Order>::depth()
{
    return dimension<RealType,Order>::depth_impl( 
is_dimension<RealType>() );
}

template<typename RealType,size_t Order>
constexpr size_t dimension<RealType,Order>::depth_impl( true_type )
{
    return 1 + RealType::depth();
}

template<typename RealType,size_t Order>
constexpr size_t dimension<RealType,Order>::depth_impl( false_type )
{
    return 1;
}