Re: [Boost-users] [units]

On Tue, Aug 30, 2011 at 6:29 AM, Michael Powell wrote:

On Tue, Aug 30, 2011 at 2:04 AM, Thomas Taylor

...

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 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.

I should clarify too, in this type of use case, we still know what the compile-time units should necessarily be. The runtime I like to think of is the user selecting: system, and possibly also unit. Which is what your aiming for here? 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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