Re: [Boost-users] [units]

Subject: Re: [Boost-users] [units]
From: Michael Powell (mwpowellnm_at_[hidden])
Date: 2011-08-30 08:29:47

On Tue, Aug 30, 2011 at 2:04 AM, Thomas Taylor
<thomas.taylor_at_[hidden]>wrote:

> Could you please review the following patch for inclusion in boost::units?
>
> *WHY*: Obviously this only defines a conversion for boost::units::one to a
> numerical 1. When trying to convert at runtime (aiming for a
> runtime/dynamic
> unit instead of the compiletime/static unit provided) I use the following
> function:
>
> template <typename U1, typename U2>
> double unit_dispatch2t(U1 const& u1, U2 const& u2) {
>    return bu::conversion_factor(u1,u2);
> }
>
> where U1 and U2 are boost::unit::unit derivatives.
>
> Without a conversion operator the compiler chickens out by claiming to not
> be able to convert boost::units::one to (in my case) double. The added
> conversion operator allows successfull compilation, thus allowing actual
> runtime units (my application needs to handle calculations where some units
> are known at compiletime and some only at runtime (e.g. the user wants the
> calculation to be done in meters or millimeters)).
>

Oh, the runtime question. Here's how we've decided to approach this.

I'll just tell you, I find the compile-time safety attractive. For runtime,
we've decided that calculations should be done in a base unit.

For anything else, we *convert to* a view unit, for display or report or
what not.

Use case: calculations on volume, pressure, etc, done in base SI units. View
may be in SI, US (English), or what have you.

HTH,
> Thomas
>
>
>
> --- one.hpp     2011-08-30 09:50:13.000000000 +0200
> +++ one2.hpp    2011-08-30 09:50:07.000000000 +0200
> @@ -19,3 +19,3 @@
>
> -struct one { one() {} };
> +struct one { one() {} operator int() { return 1; } };
>
>
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