Multiple dispatch in an inner method

General Usage
4

Here’s what I coalesced on, so far:

abstract type AbstractPeriod end

abstract type Instantaneous <: AbstractPeriod end

abstract type Prolonged <: AbstractPeriod end

abstract type POIType{T <: AbstractPeriod} end

for i in (:Nest, :Feeder)
    @eval struct $i <: POIType{Instantaneous} end
end

for i in (:Track, )
    @eval struct $i <: POIType{Prolonged} end
end

abstract type DurationType{T <: AbstractPeriod} end

struct Interval <: DurationType{Prolonged}
    anchor::Nanosecond
    duration::Nanosecond
end

struct Instant <: DurationType{Instantaneous}
    anchor::Nanosecond
end

struct POI{P <: POIType, D <: DurationType}
    type::P
    temporal::D
    POI(type::P, temporal::D) where {T <: AbstractPeriod, P <: POIType{T}, D <: DurationType{T}} = new{P, D}(type, temporal)
end