[julia-users] reason for inner constructor in Dates

[Tamas Papp]

Hi,

I am reading the code of Base libraries to improve my understanding and
style. In base/dates/types.jl, I noticed

for T in (:Year,:Month,:Week,:Day)
    @eval immutable $T <: DatePeriod
        value::Int64
        $T(v::Number) = new(v)
    end
end

which expands to code like

immutable Year <: DatePeriod
  value::Int64
  Year(v::Number) = new(v)
end

I have a simple question: what is the reason for defining the inner
constructor? Wouldn't

immutable Year <: DatePeriod
  value::Int64
end

automatically define one, except for restricting to ::Number? If that is
the reason, I would like to understand why.

Best,

Tamas