HessianTracer type improvements

[gdalle]

SparseConnectivityTracer.jl/src/tracers.jl

Lines 119 to 121 in 83cb0b0

	struct HessianTracer{S} <: AbstractTracer
	inputs::Dict{UInt64,S}
	end

Would it be more coherent to have keys of type eltype(S), since they are also indices, rather than always UInt64?

[adrhill]

Sounds good. :)

[gdalle]

As seen in #45, we should also

• make the AbstractDict subtype parametric, e.g. to use SortedDict in conjunction with SortedVector
• rename the type parameter T to I for integer wherever it still appears
• add an inner constructor that checks eltype(S) == I