Re: [boost] Boost Units library preview

From: Andy Little (andy_at_[hidden])
Date: 2006-08-21 20:20:50

"Dave Steffen" <dgsteffen_at_[hidden]> wrote in message
news:17642.19283.854773.973499_at_yttrium.numerica.us...

> I don't know how to do that, but I'm absolutely sure it's what your
> users want.

Sorted as a quick test in my local copy of Quan FWIW.

I added a metafunction to query the unit :

allow_implicit_unit_conversions<StaticUnit>::type // bool_ true or false

 (of fixed_quantity<StaticUnit,NumericType>)

Modified the fixed_quantity ctor to query the unit.

added a conditional explicit ctor allowing conversions and voila:

#include <quan/length.hpp>

int main()
{
    quan::length::m L1(1);
    quan::length::mm L2 = L1; // line 6
    L1 + quan::length::m(L2); // ok
}

e:\Projects\Test\test.cpp(6) : error C2440: 'initializing' : cannot convert from
'quan::length_<Value_type>::m' to 'quan::fixed_quantity<StaticUnit,NumericType>'
        with
        [
            Value_type=quan::quantity_traits::default_value_type
        ]
        and
        [
            StaticUnit=quan::meta::unit<quan::meta::components::of_length::abstract_quantity,quan::meta::si_unit::milli>,
            NumericType=quan::quantity_traits::default_value_type
        ]
        Constructor for class 'quan::fixed_quantity<StaticUnit,NumericType>' is
declared 'explicit'
        with
        [
            StaticUnit=quan::meta::unit<quan::meta::components::of_length::abstract_quantity,quan::meta::si_unit::milli>,
            NumericType=quan::quantity_traits::default_value_type
        ]

Also works for addition etc.

In this quick mod a Macro decides whether the particular implementation of a
StaticUnit returns true or false.
but you could create a Static where that is a policy parameter I guess.. I'm not
sure if this is important enough to do that, but if it is, it is no great
problem to add it.

regards
Andy Little