Allow subtracting two thermodynamic temperatures

[ISibboI]

Hi, thanks for making uom! It has caught a few errors already in my small hobby project.

Currently, when I subtract two thermodynamic temperatures, I get the following error:

error[E0308]: mismatched types
   --> src\substance\water.rs:122:57
    |
122 |         let temperature_difference = self.temperature - target_temperature;
    |                                                         ^^^^^^^^^^^^^^^^^^ expected trait `Kind`, found trait `TemperatureKind`
    |
    = note: expected struct `Quantity<dyn Dimension<I = Z0, J = Z0, Kind = dyn Kind, L = Z0, M = Z0, N = Z0, T = Z0, Th = ...>, ..., ...>`
               found struct `Quantity<dyn Dimension<I = Z0, J = Z0, Kind = ..., L = ..., M = ..., N = ..., T = ..., Th = ...>, ..., ...>`

However, I would expect this to work and the result to be a TemperatureInterval.

[jacg]

See

• Subtracting thermodynamic temperatures should produce a temperature interval #380
• Computing an average temperature #403
• Distinguishing affine and vector quantities #289

[ISibboI]

How about adding another type parameter to Quantity that specifies if it can be added/subbed with itself or not? Then the default add/sub impl can be made only for some default value of that type parameter, and ThermodynamicTemperature could get its own implementation by having another value for this type parameter.

[iliekturtles]

Closing as a duplicate of #380.