Quantity types aren't Unpin

[Michael-F-Bryan]

I'm trying to use uom types in an async context and found that quantities are !Unpin.

Types like uom::si::f64::Velocity are meant to be identical to a normal float, so it should be perfectly fine for them to be Unpin. I'm guessing the offending part is the use of dyn trait objects that don't have + Unpin in their trait bounds.

This was found on uom 0.29.0 and rustc version 1.48.0-nightly (397b390cc 2020-08-27).

Here's a minimal test case:

#[test]
fn velocity_should_be_unpin() {
    fn assert_unpin<T: Unpin>() {}

    assert_unpin::<uom::si::f64::Velocity>();
}

And it fails with this compilation error:

error[E0277]: `(dyn uom::si::Dimension<T = uom::typenum::NInt<uom::typenum::UInt<uom::typenum::UTerm, uom::typenum::B1>>, I = uom::typenum::Z0, N = uom::typenum::Z0, L = uom::typenum::PInt<uom::typenum::UInt<uom::typenum::UTerm, uom::typenum::B1>>, Kind = (dyn uom::Kind + 'static), M = uom::typenum::Z0, J = uom::typenum::Z0, Th = uom::typenum::Z0> + 'static)` cannot be unpinned
  --> indexer\src\systems\motion\manual_mode.rs:94:9
   |
92 |         fn assert_unpin<T: Unpin>() {}
   |                            ----- required by this bound in `systems::motion::manual_mode::tests::velocity_should_be_unpin::assert_unpin`
93 |
94 |         assert_unpin::<uom::si::f64::Velocity>();
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ within `uom::si::Quantity<(dyn uom::si::Dimension<T = uom::typenum::NInt<uom::typenum::UInt<uom::typenum::UTerm, uom::typenum::B1>>, I = uom::typenum::Z0, N = uom::typenum::Z0, L = uom::typenum::PInt<uom::typenum::UInt<uom::typenum::UTerm, uom::typenum::B1>>, Kind = (dyn uom::Kind + 'static), M = uom::typenum::Z0, J = uom::typenum::Z0, Th = uom::typenum::Z0> + 'static), (dyn uom::si::Units<f64, thermodynamic_temperature = uom::si::thermodynamic_temperature::kelvin, mass = uom::si::mass::kilogram, amount_of_substance = uom::si::amount_of_substance::mole, electric_current = uom::si::electric_current::ampere, length = uom::si::length::meter, luminous_intensity = uom::si::luminous_intensity::candela, time = uom::si::time::second> + 'static), f64>`, the trait `std::marker::Unpin` is not implemented for `(dyn uom::si::Dimension<T = uom::typenum::NInt<uom::typenum::UInt<uom::typenum::UTerm, uom::typenum::B1>>, I = uom::typenum::Z0, N = uom::typenum::Z0, L = uom::typenum::PInt<uom::typenum::UInt<uom::typenum::UTerm, uom::typenum::B1>>, Kind = (dyn uom::Kind + 'static), M = uom::typenum::Z0, J = uom::typenum::Z0, Th = uom::typenum::Z0> + 'static)`
   |
   = note: required because it appears within the type `std::marker::PhantomData<(dyn uom::si::Dimension<T = uom::typenum::NInt<uom::typenum::UInt<uom::typenum::UTerm, uom::typenum::B1>>, I = uom::typenum::Z0, N = uom::typenum::Z0, L = uom::typenum::PInt<uom::typenum::UInt<uom::typenum::UTerm, uom::typenum::B1>>, Kind = (dyn uom::Kind + 'static), M = uom::typenum::Z0, J = uom::typenum::Z0, Th = uom::typenum::Z0> + 'static)>`
   = note: required because it appears within the type `uom::si::Quantity<(dyn uom::si::Dimension<T = uom::typenum::NInt<uom::typenum::UInt<uom::typenum::UTerm, uom::typenum::B1>>, I = uom::typenum::Z0, N = uom::typenum::Z0, L = uom::typenum::PInt<uom::typenum::UInt<uom::typenum::UTerm, uom::typenum::B1>>, Kind = (dyn uom::Kind + 'static), M = uom::typenum::Z0, J = uom::typenum::Z0, Th = uom::typenum::Z0> + 'static), (dyn uom::si::Units<f64, thermodynamic_temperature = uom::si::thermodynamic_temperature::kelvin, mass = uom::si::mass::kilogram, amount_of_substance = uom::si::amount_of_substance::mole, electric_current = uom::si::electric_current::ampere, length = uom::si::length::meter, luminous_intensity = uom::si::luminous_intensity::candela, time = uom::si::time::second> + 'static), f64>`

In my real code, the compiler suggests using #![feature(trivial_bounds)] (rust-lang/rust#48214).

    = note: required because it appears within the type `systems::motion::manual_mode::ManualMode`
    = help: see issue #48214
    = help: add `#![feature(trivial_bounds)]` to the crate attributes to enable

[iliekturtles]

Completed by #205. Had to manually merge the PR.