improve type stability?

[stevengj]

Currently, it seems like most of the operations are type-unstable:

julia> using SIUnits, SIUnits.ShortUnits, Base.Test

julia> @inferred 1m
ERROR: return type SIUnits.SIQuantity{Int64,1,0,0,0,0,0,0,0,0} does not match inferred return type Union{Int64,SIUnits.SIQuantity{T<:Number,m,kg,s,A,K,mol,cd,rad,sr}}
 in error(::String) at ./error.jl:21
 in error(::String) at /Applications/Julia-0.5.app/Contents/Resources/julia/lib/julia/sys.dylib:?

julia> x = 1m
1 m

julia> @inferred x*x
ERROR: return type SIUnits.SIQuantity{Int64,2,0,0,0,0,0,0,0,0} does not match inferred return type Union{Int64,SIUnits.SIQuantity{T<:Number,m,kg,s,A,K,mol,cd,rad,sr}}
 in error(::String) at ./error.jl:21
 in error(::String) at /Applications/Julia-0.5.app/Contents/Resources/julia/lib/julia/sys.dylib:?

It seems like there is enough information available to determine these exponents at compile time.

[stevengj]

I was playing around with it, and generated functions seem capable of doing this nicely.

[timholy]

This already works today in Unitful, which has many other nice goodies besides.

[stevengj]

Ah, I see... I guess SIUnits is obsolete then?

[timholy]

It still works and remains an impressive package, but

• Unitful was written at a time it could take advantage of newer features of Julia (SIUnits accomplished amazing things at an early stage of Julia's evolution)
• @ajkeller34 has put, and continues to put, a lot of active maintenance into Unitful
• there's only so much manpower

[stevengj]

Sure, but it would be nice if packages that are superseded by newer packages would be clearly marked as such, e.g. on pkg.julialang.org and in the first sentence of the README.