Implement operations for Quantity references about uom

[jacg]

Are there any difficulties or pitfalls here, or is it just a fairly mechanical process that simply requires finding the time to do it?

If it's the latter, I'll start chipping away at it.

If it's the former, I could also have a go, if you brief me.

[iliekturtles]

Should be completely mechanical.

Implementation would start with the following macros

uom/src/system.rs

Lines 588 to 591 in 66d3e85

	impl_ops!(Add, add, +, AddAssign, add_assign, +=, Sum,
	Mul, mul, *, MulAssign, mul_assign, *=, add_mul);
	impl_ops!(Sub, sub, -, SubAssign, sub_assign, -=, Diff,
	Div, div, /, DivAssign, div_assign, /=, sub_div);

And you can compare against what the standard library is doing for inspiration on implementing for T and &T. https://doc.rust-lang.org/src/core/ops/arith.rs.html#117-133

Once the major traits are implemented we can go hunting to see if there is anything else like Sub that needs extra impls.

[jacg]

Implementation would start with the following macros [impl_ops!]

Just to be sure: Are you suggesting to add the implementations of the reference versions, to the bodies of those macros?

I don't quite understand the pattern inside the macro. First we have this group of 4:

• ....autoconvert! ... AddSubTrait
• not_autoconvert! ... AddSubTrait
• ....autoconvert! ... AddSubAssignTrait
• not_autoconvert! ... AddSubAssignTrait

followed by another group of 4:

• ....autoconvert! ... MulDivTrait
• not_autoconvert! ... MulDivTrait
• ................ ... MulDivTrait
• ................ ... MulDivAssignTrait

Why is there an asymmetry between the AddSub group and the MulDiv group?

[iliekturtles]

I apologize for taking so long to get to this. I'll look at the PR in a second to see what you've done so far. The original thought was to do something to the standard library and use a macro that accepts the type (T vs. &T) as a parameter.

The asymmetry is because multiply and divide allow for operating on the underlying storage type as well as the quantity. e.g. length * time and length * 3.0. Add/subtract require the same quantity on both sides of the operator. e.g. length1 + length2. The [not_]autoconvert! macros decide if the implementation supports operating on quantities with different base units.