Re: [Boost-users] [EXTERNAL] [ Boost.Units ] Invert a quantity_type

Subject: Re: [Boost-users] [EXTERNAL] [ Boost.Units ] Invert a quantity_type
From: Belcourt, Kenneth (kbelco_at_[hidden])
Date: 2017-06-09 15:41:36

> On Jun 8, 2017, at 1:51 PM, Steven Watanabe via Boost-users <boost-users_at_[hidden]> wrote:
> 
> AMDG
> 
> On 06/06/2017 05:12 PM, Belcourt, Kenneth via Boost-users wrote:
>> 
>> I have a structure that is passed some type from which I can extract a units quantity type:
>> 
>> <snip>
>> 
>> Is there a way to invert a quantity type so I can compute and return, say, the inverse of the passed quantity_type?  So, for example, is there any Boost.Units inverse meta like function that might let me say something like this:
>> 
>> <snip>
>> I’m hoping for something more general than partially specializing the bu::inverse method for each quantity I may want to invert.  Any ideas?
>> 
> 
> There isn't a specific inverse function, but,
> shouldn't divide_typeof_helper work or
> power_typeof_helper<T, -1> work?  (or better
> just use decltype)

Sure, thought about using the helper functions, but they’re all marked as non-public APIs.

/// INTERNAL ONLY
template<class System,
         class Dim,
         class X>
struct divide_typeof_helper< X,unit<Dim,System> >

So don’t want to depend on bu implementation details.

As for decltype, that’s possibly a bridge too far for less experienced developers so, for now, I still prefer explicit typing where I can.

I appreciate the help Steven, thanks for suggestions!