DecayModel.halfLifeNumberProperty doesn't support "unknown" half lives

[zepumph]

Found while handling a TODO in #93. If unknown, then that Property should be null (from AtomIdentifier), but that isn't supported or expected from its TypeScript implementation.

[zepumph]

It isn't clear what the desired behavior is for the halfLifeNumberProperty when it reaches unknown. @Luisav1 let me know if you want assistance on this.

[Luisav1]

If the half-life is null (aka "unknown") then the half-life is set to -1 when the halfLifeNumberProperty is set.

build-a-nucleus/js/decay/model/DecayModel.ts

Lines 51 to 54 in f2b033a

	// the nuclide is unstable and its half-life data is missing, set -1 as the half-life as a placeholder
	else if ( AtomIdentifier.getNuclideHalfLife( protonNumber, neutronNumber ) === null ) {
	halfLife = -1;
	}

Then this is dealt with appropiatly in the listener:

build-a-nucleus/js/decay/view/HalfLifeNumberLineNode.ts

Lines 268 to 276 in 74f8279

	// the nuclide is unstable but the half-life data is unknown
	else if ( halfLifeNumber === -1 ) {
	showHalfLifeArrow( false );
	halfLifeUnknownText.visible = true;
	halfLifeNumberText.visible = false;
	this.moveHalfLifePointerSet( 0, options.isHalfLifeLabelFixed );
	}

The use of -1 as a placeholder can be done in AtomIdentifier instead though like below, is this something we want to do?

  // Get the half-life of a nuclide with the specified number of protons and neutrons.
  getNuclideHalfLife: function( numProtons: number, numNeutrons: number ): number | null | undefined {
    if ( !HalfLifeConstants[ numProtons ] ) {
      return undefined;
    }
    else if ( HalfLifeConstants[ numProtons ][ numNeutrons ] === null ) {
      return -1;
    }
    return HalfLifeConstants[ numProtons ][ numNeutrons ];
  },

[zepumph]

I think the issue to solve here is that the terms undefined and null are codified values that mean something, but are not documented. I believe that the work to be done is to document the possible results returned by the function (a half life number, no half life, or an unknown half life), and then the corresponding code values of each. I think of it as a bug that undefined and null mean two different things, and I think that -1 would do a good job of representing an unknown half life.

Also if you would like my response or assistance on an issue please re-assign me so I don't lose it (which I am very good at doing).

[zepumph]

Discussed with @Luisav1, let's also change null -> -1 in HalfLifeConstants too.

• Update doc
• remove the mapping from null -> -1 in the getter function.

[zepumph]

After finding this data null = unknown duplicated in the DECAYS_INFO_TABLE as well, I think it may just be easiest to keep things as is. Closing