Hello Experts!
After reading Julia docs on types it is still unclear for me how how to use
singleton classes for common tasks, e.g. for packaging some common values.
As a side note let me elaborate with the example from Scala programming
language.
Scala has intrinsic support for singletons - Objects.
```scala
scala> object CParam {
| var rho: Double = 1.0
| var cc: Double = 1.0
| }
defined module CParam
scala> CParam.rho = 2.0
CParam.rho: Double = 2.0
scala> import CParam._
import CParam._
scala> rho
res0: Double = 2.0
```
Now trying to project it to Julia:
```jlcon
julia> type CParam
rho::Float64
cc::Float64
function CParam()
new(0.0, 0.0)
end
end
julia> x = CParam()
CParam(0.0,0.0)
julia> x.rho
0.0
```
So good so far, though this is not a singleton, just an instance.
The Julia documentation says that parametric Type{T} is a special
parametric kind of the type T - the singleton type.
```jlcon
julia> x = Type{CParam}
Type{CParam}
julia> x.rho
ERROR: type DataType has no field rho
```
Trying to exploit modules as model for singleton class (follow Fortran90 -
it uses modules for information hiding and packaging).
```jlcon
julia> module CParam
export rho, bulk, cc, zz
rho = 1.0
bulk = 1.0
cc = 1.0
zz = 1.0
end
julia> CParam.rho = 2.0
ERROR: cannot assign variables in other modules
```
Could you please recommend a programming idiom better fitting to Julia?
Thanks!
Alexander
