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nice! But for some reason I believe this would work for argument functions

double f(quantitysi::length v){ return 1.;} ... quantitycgs::lengh A = 4.*cgs::centimeter f(A); // doesn't work! not matching function

why is this? isn't the argument of the call a sort of construction argument for the function argument, or is more like a plain assignment. Is there a way to force the automatic conversion of the function call.

Or I am forced to use this other long call?

f(quantitysi::length(A));

Yes. The constructor is explicit.

Or you can write it as a template function that takes any argument that is a quantity of length : #include <iostream> #include #include #include using namespace boost::units; template Y f(quantity,Y> v) { const Y w = quantitysi::length,Y(v).value(); std::cout << v << "\t" << w << std::endl; return w; } int main(void) { f(quantitycgs::length,double(17.0*cgs::centimeters)); return 0; } Matthias

On 3/25/2011 10:40 AM, alfC wrote:

On Mar 25, 9:46 am, Matthias Schabel wrote:

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nice! But for some reason I believe this would work for argument functions

...

...

double f(quantitysi::length v){ return 1.;} ... quantitycgs::lengh A = 4.*cgs::centimeter f(A); // doesn't work! not matching function

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...

why is this? isn't the argument of the call a sort of construction argument for the function argument, or is more like a plain assignment. Is there a way to force the automatic conversion of the function call.

...

...

Or I am forced to use this other long call?

...

...

f(quantitysi::length(A));

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Yes. The constructor is explicit.

thanks for the clarification

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Or you can write it as a template function that takes any argument that is a quantity of length : [...code...]

Thank you for the suggestion, the problem is that a nice looking function such as

void f( quantity<volume> v, quantity<temperature> t, quantity<length> l ){ ... use v, l, t in a given controlled set of units }

transfroms into this mess,

template< class VolumeUnit, class TemperatureUnit, class LengthUnit

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void f( quantity<VolumeUnit> v_, quantity<TemperatureUnit> t_, quantity<LengthUnit> l_ ){ quantity<volume> v(v); quantity<temperature> t(t_); quantity<length> l(l_); ... use v, l, t in a given controlled set of unit }

just to obtain the same effect. and that without even static asserting that XXXUnit is_unit.

Not usually. If your equations are dimensionally coherent, and not empirical, you can generally do without a lot of what you just showed. For example, one might be tempted to write the head/pressure conversion as: quantitysi::pressure head_to_press( quantitysi::length head , quantitysi::mass_density den ) { quantitysi::acceleration g = 9.80665 * si::meters_per_second_squared return head * den * g; } All you really need to do though is: template < typename System, typename T > quantity< unit head_to_press( quantity< unit, T> head , quantity< unit, T> den ) { quantity< unit, T> g(9.8066 * si::meters_per_second_squared); return head * den * g; } The only part you have to do explicit conversions on is your constants. Of course, when dealing with empirical equations you've got a different thing going on. More often than not you have to break out of the units anyway and use the "unsafe" operations like ::from_value.