I find myself repeating a somewhat cumbersome type declaration, which seems like something to avoid. How? Here’s a condensed version of my current code, which uses `Vector{Union{Missing, IntervalBox{1, Float64}}}`

twice.

```
"enumerate desired calculation for WorkArea"
# implicit value assignment starts at 0. But I want to use these as array indices
# and julia arrays are 1-based.
@enum Objective justZ=1 justW=2 WZ=3 just1=4
"""
Working data for a particular thread.
"""
mutable struct WorkArea{TEvaluator,TSegs}
# ... many fields omitted
"record details of the integration. Int(Objective) has result for that Objective"
intervals::Vector{Union{Missing, IntervalBox{1, Float64}}}
end
"convenient constructor"
function WorkArea(dat::DataFrame, ev::TEvaluator) where {TEvaluator}
zip::UInt = 0
WorkArea(dat, dat.Y, ev, work(ev), WZ, zip, zip, zip, Vector{Union{Missing, IntervalBox{1, Float64}}}(missing, 4))
end
```

I think the type in the constructor is mandatory to get the correct type; I could omit it from the `struct`

definition, with perhaps some loss of efficiency.

I looked for something that would give me the type of a component of a `struct`

, something like `typeof(Workarea.intervals)`

, but didn’t find it.