The repo https://github.com/LaGuer/PhysicalConstant.jl has a list of physical constants, some of which could be considered. Note: The names of constants should be discussed. As a practical matter, using a name like c for speed of light can be confusing in code where someone might not realize that c is a physical constant as opposed to a local variable.

I'm not sure this is useful but it should be discussed.

After the unit system has been set, my feeling is that setunits should not change the unit system unless unitsystem is explicitly set. For example:

julia> setunits(:CGS)
julia> setunits(time = :us)   # This will reset the units system to the default!

We need to add functionality to change the units of all the constants to any other common unit.
The plan is to have all the constants stored in consistent units, (base eV), and use conversion to create temporary copies of the units in local memory. Since this total a few hundred Float64 objects, it won't take up more than a few kB

Per David, there is no need to change the units of constants that are only used 'under the hood' which is to say, in the simulation.
This means that we don't need a global constants: instead, we want functions like mass_of(), or velocity_of(), which take in an object and return a number for viewing, rather than for computation.

I've added a new type to ParticleTypes.jl that has name, charge, mass, spin, and anomalous magnetic moment attributes. A good
(and extremely simple) task is to write a function for each numeric attribute that takes in the TrackedSpecies object and a unit type, and if possible returns the attribute in the requested units.
After this, there should be a collection of functions that handle all the dimensionful constants in PhysicalConstants.jl that are not associated directly to particles, eg c_light and h_planck.

It turns out the desired functionality is way simpler than what you were trying to do earlier... whoopsie.

One thing that is desired is the ability to specify the units for the constants. before the constants are instantiated.

massof and chargeof functions use conversion factors current_units.charge.conversion and current_units.mass.conversion. This is potentially computationally slow. Better would be to have current_units.charge_conversion and current_units.mass_conversion which are can be defined to have definite types.

Julia version 1.10.0:

julia> using AtomicAndPhysicalConstants
Precompiling AtomicAndPhysicalConstants
Info Given AtomicAndPhysicalConstants was explicitly requested, output will be shown live
┌ Warning: Replacing docs for AtomicAndPhysicalConstants.Particle :: Union{} in module AtomicAndPhysicalConstants
└ @ Base.Docs docs/Docs.jl:243
┌ Warning: Replacing docs for AtomicAndPhysicalConstants.Particle :: Union{} in module AtomicAndPhysicalConstants
└ @ Base.Docs docs/Docs.jl:243
WARNING: Method definition (::Type{AtomicAndPhysicalConstants.Particle})(AbstractString, Int32, Float64, Float64, Float64) in module AtomicAndPhysicalConstants at /Users/dcs16/.julia/dev/AtomicAndPhysicalConstants/src/ParticleTypes.jl:28 overwritten on the same line (check for duplicate calls to include).
ERROR: Method overwriting is not permitted during Module precompilation. Use __precompile__(false) to opt-out of precompilation.
? AtomicAndPhysicalConstants
[ Info: Precompiling AtomicAndPhysicalConstants [5c0d271c-5419-4163-b387-496237733d8b]
┌ Warning: Replacing docs for AtomicAndPhysicalConstants.Particle :: Union{} in module AtomicAndPhysicalConstants
└ @ Base.Docs docs/Docs.jl:243
┌ Warning: Replacing docs for AtomicAndPhysicalConstants.Particle :: Union{} in module AtomicAndPhysicalConstants
└ @ Base.Docs docs/Docs.jl:243
WARNING: Method definition (::Type{AtomicAndPhysicalConstants.Particle})(AbstractString, Int32, Float64, Float64, Float64) in module AtomicAndPhysicalConstants at /Users/dcs16/.julia/dev/AtomicAndPhysicalConstants/src/ParticleTypes.jl:28 overwritten on the same line (check for duplicate calls to include).
ERROR: Method overwriting is not permitted during Module precompilation. Use __precompile__(false) to opt-out of precompilation.
[ Info: Skipping precompilation since precompile(false). Importing AtomicAndPhysicalConstants [5c0d271c-5419-4163-b387-496237733d8b].
┌ Warning: Replacing docs for AtomicAndPhysicalConstants.Particle :: Union{} in module AtomicAndPhysicalConstants
└ @ Base.Docs docs/Docs.jl:243
┌ Warning: Replacing docs for AtomicAndPhysicalConstants.Particle :: Union{} in module AtomicAndPhysicalConstants
└ @ Base.Docs docs/Docs.jl:243
┌ Warning: Replacing docs for AtomicAndPhysicalConstants.Particle :: Union{} in module AtomicAndPhysicalConstants
└ @ Base.Docs docs/Docs.jl:243
┌ Warning: Replacing docs for AtomicAndPhysicalConstants.SubatomicSpecies :: Union{} in module AtomicAndPhysicalConstants
└ @ Base.Docs docs/Docs.jl:243
┌ Warning: Replacing docs for AtomicAndPhysicalConstants.AtomicSpecies :: Union{} in module AtomicAndPhysicalConstants
└ @ Base.Docs docs/Docs.jl:243

Need a function (or functions) to:

• List names and values of the physical constants. EG: showconst(:physical) or showconst()
• List isotopes and masses of a given atomic species. EG: showconst(:Fe)
• List of atomic species - Name and symbol. EG: showconst(:atomic)

There needs to be a way to label a particle to be a photon.

Anyone object to eliminating tabs and using two spaces per indent?

Needed is a way to define antiatoms. My suggestion is to use an "anti_" prefix like "anti_He" rather than something like "He_bar" as not intuitive. Something like "antiHe" looks too jumbled.

Also a function antiparticle(particle) is helpful.

Note: The massof function when calculating the mass needs to take into account that for an anti-atom the nucleus is surrounded by positrons and not electrons.

find references for the dipole moment of a proton, a neutron, a deuteron, and He3 from PDG. Write a code to pull down the measured moment and get the anomalous part of it, returning a vector.

• The using statements should all be in one place (EG: AtomicAndPhysicalConstants.jl).
• Is Dates package even used?
• Dates is not in the dependency list so when I try using AtomicAndPhysicalConstants I get a load error.

That is Particle("#3He+") and Particle("C+3") are handled along with the present syntax. This is useful since the user can then specify a particle using just a single string. Essentially, the Particle function can look for characters "#", "+", or "-" and split the string as appropriate.