Context-dependent quantity_cast with struct?

[haborite]

I find quantity_cast quite useful. Looking through some of the issues, it seems that many uses of quantity_cast are tied to specific contexts—especially when dealing with fundamental physical objects.

Given that, I wonder if using structs could help make these conversions safer. If Numbat were to support something like Rust-style impl syntax in the future, perhaps we could write things like following:

struct Photon {
    energy: Energy 
}

impl Photon {

    fn from(input: D) -> Self {
	match type(D) {
	    Energy   => Self { energy: input } # from energy
	    Length   => Self { energy: c × planck_constant ÷ input } # from wavelength
	    Length⁻¹ => Self { energy: c × planck_constant × input } # from wavenumber
            Time⁻¹   => Self { energy: planck_constant × input } # from frequency
            _        => **raise some error**
	}
    }

    fn energy(&self) -> Energy { .. }
    fn wavelengty(&self) -> Length { .. }
    fn wavenumber(&self) -> Length⁻¹ { .. }
    fn frequency(&self) ->  Time⁻¹ { .. }
}

let photon = Photon(400 nm)
photon.energy() --> eV
# 2.497 eV
photon.frequency() --> Hz
# 7.5 × 10e14 Hz

For common objects like Photon or Electron, I think there might even be value in including them in the standard library.

This isn’t a feature request—just an idea I wanted to share. I’d love to hear what others think.

[sharkdp]

Why did you close this discussion? This sounds like a great idea! impl blocks are definitely on the roadmap!

[haborite]

Thank you for the comment!
I mistakenly thought that this issue had already been discussed, so I closed it.
I've reopened the discussion.