[wpiunits] Add absolute value and copy sign functionality

[viggy96]

Absolute value and copy sign are some common methods that I use, its kinda annoying to need to unwrap the object to do these common operations.

[calcmogul]

These operations do not make sense on an element of the SO(2) group. Rotation2d is a 2D unit vector, not an Euler angle. If you want an Euler angle, use a double or Angle.

The internal value field should be treated as if it doesn't exist, since it's a hack to prevent implicit wrapping in the constructor. Any operations on the Rotation2d don't preserve it. I’ve wanted to get rid of the value field, but I was told we couldn’t because it would break too much user code, but it will be removed for 2027. We originally took it from 254's geometry library, but they didn't intend the value field to be used in this way either; we just didn't realize that at the time: https://www.chiefdelphi.com/t/possible-bugs-in-rotation2d-and-rotation3d-java/474140/11

[viggy96]

Should the methods be removed then, or should I instead be operating using getRadians() and Rotation2d.fromRadians(double) instead of m_value?

[calcmogul]

The functions should be removed from Rotation2d. I have no opinion on them being in the measure class though. Rust takes that extension method approach as opposed to providing free functions.

[calcmogul]

This would ideally be called signum() and have the same semantics as the Java standard library.

[viggy96]

This is slightly different than signum(). Math.signum() simply returns +1, 0 or -1 based on the sign of the input. This method copies the sign of the input variable, but maintains the magnitude.
Its similar to Math.copySign().
https://docs.oracle.com/javase/8/docs/api/java/lang/Math.html#copySign-double-double-

[calcmogul]

This function returns the wrong result if this is nonzero and other is zero. It inverts the sign when it shouldn't since the signum() return values don't match.

You should probably just use Math.copySign() on the base unit magnitude.

[viggy96]

Hmm, I get an error when I try to use Math.copySign().
Type mismatch: cannot convert from Measure<capture#1-of ?> to Measure<U>

/**
   * Take the sign of another measure.
   * @param other measure from which to take sign
   * @return a new measure with the sign from another measure
   */
  default Measure<U> copySign(Measure<U> other) {
    return baseUnit().of(Math.copySign(this.baseUnitMagnitude(), other.baseUnitMagnitude()));
  }

But if I do

if (other.isEquivalent(baseUnit().zero()) && baseUnitMagnitude() < 0.0) return times(-1);
else return times(other).baseUnitMagnitude() >= 0.0 ? this : times(-1);

its fine.

[SamCarlberg]

Unit.of returns a wildcarded Measure<?> because the self-type isn't known. You'd need to cast to Measure<U>.

Another issue is nonlinear units. What's the absolute value of -10°C? Using the base unit (Kelvin), it's still -10°C (263.15K); but using the relative unit Celsius it'd be 10°C, which would be treated as 283.15K in any math operations

[viggy96]

Perhaps abs() should also take in the desired Unit?
Also, how would I resolve an unchecked cast for the wildcard Measure<?> ?

[viggy96]

Is there anything else needed for this to be merged?