On Feb 28, 2:06 am, Samuel Debionne wrote:

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I have been playing with things like :

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quantity  >

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That won't work because variant<...>  is not a unit type. Can you post a small example of what you want to achieve?

Of course it won't work as is. But I did a bit of hacking in this direction.

the reason I asked for an example is because I was working in something similar (not the same though).

My aim is to be able to write something like this :

any_quantity any_q = myfunction(...);

...

quantity<force> = any_q; //runtime check

I think those quantities are so unrelated with each other from a "type" point of view that you would be better of using templates. Actually I do this a lot: template<class Unit> myfunction(quantity<Unit> q){ ... } and also (if possible) auto q = myfunction( ...);

Is there any plan to have a runtime layer above Boost.Units (like boost GIL have dynamic any_images, any_view...) ?

I think this goes against the library design which is to be zero overhead. (But it may be useful some times although my pattern above is a good competition against your requested feature) What I was working on is something like: any_quantity that can hold any quantity with force dimension, this makes more sense to me because at least I know the all force quantities are potentially convertible to one another, regardless of the unit system. In my proposal there is no runtime checking at all, but only runtime conversions. Good Luck, Alfredo

It would check the maximum at compile time (basically check if one the variant type could match the target quantity unit) and delegates the real check at runtime (throwing an exception if the conversion fails) ?

IMHO it would be a lovely addition to the current library.

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Alfredo, Thank you for your answers. To be more pragmatic here is an archetype of function that I have in my problem : any_quantity myfunction(energy_q arg1) { if (arg1 > 1.0 * jouls) return 2.2 * newtons; else return 3.3 * meters; } That may sound weird but it's a real case. I'm solving a problem with two quantities that have unrelated units and one quantiy or the other is choosen at runtime depending on some state variable values. Ultimately those quantities are stored in a single matrix. For now I break the dimensionnal analysis at this step using plain doubles.

I think this goes against the library design which is to be zero overhead. (But it may be useful some times although my pattern above is a good competition against your requested feature)

What I was working on is something like:

any_quantity

that can hold any quantity with force dimension, this makes more sense to me because at least I know the all force quantities are potentially convertible to one another, regardless of the unit system. In my proposal there is no runtime checking at all, but only runtime conversions.

Runtime conversion are also something I am interrested. Are you following the lead of : http://www.boost.org/doc/libs/1_46_0/doc/html/boost_units/Examples.html#boos... I think that we could layer things this way : LAYER 3: any_quantity runtime dimensional analysis and conversion LAYER 2: any_quantity compile time dimensional analysis and runtime conversion LAYER 1: quantity<unit> the actual library Each extension layers could be build on top of the others. For performance reason, the runtime dimensional analysis could be switched off for release build.

In any case I would like to know of any solution you can come up with.

Of course.