Unitless quantities should convert to primitives

[nickbabcock]

I expected something along the lines of the following to work:

let start = Time::new::<second>(1.0);
let end = Time::new::<second>(10.0);
let interval = Time::new::<second>(3.0);

let buckets: f32 = ((end - start) / interval).into()

I'm curious if I'm missing something, as I'm still exploring the library. Currently the workaround seems to be

(end - start).get(second) / interval.get(second)

Which isn't as pretty 😄

[iliekturtles]

The way to do this right now is to directly access the value member of the Quantity struct. However I would like to make value private in the future so a better way is needed.

I haven't put much thought into dimensionless quantities at this point as I wanted to complete #3. This issue touches on dimensionless quantities because similar to the difference between ThermodynamicTemperature and TemperatureInterval there are multiple distinct dimensionless types: Ratio, as seen here, but also types like Angle (m/m) and PowerEfficiency (W/W).

I'll leave the issue open with the intention of implementing impl<U, V> From<V> for Quantity<DimensionOne, U, V>.

    let start = Time::new::<second>(1.0);
    let end = Time::new::<second>(10.0);
    let interval = Time::new::<second>(3.0);

    let buckets: f32 = ((end - start) / interval).value;

    println!("{}", buckets);

[nickbabcock]

The temporary workaround worked great. uom helped me solve a couple head scratching bugs.

I'm excited for when dimensionless quantities become first class citizens 😄

[iliekturtles]

Awesome! Glad to hear it helped solve some problems for you!

[shradej1]

Is there a dimensionless unit that can be used to get at the value in a unit-safe way? Like,

let buckets: f32 = ((end - start) / interval).get(unit);

[iliekturtles]

Not yet, but there will be "soon." I have most of the changes complete in the dev-ratio branch to create a new Ratio quantity. You'll be able to do the following once it is merged:

let buckets: f32 = ((end - start) / interval).get(ratio);

[shradej1]

That's great! An Into conversion to primitives might be nice too, but I think the ratio approach is a more consistent treatment.

[iliekturtles]

From/Into will also be available for Ratios once changes are merged into master!

uom/src/si/ratio.rs

Line 35 in 7dec1f1

impl<U, V> ::lib::convert::From<V> for Ratio<U, V>