Addition/subtraction for some `AnchoredInterval`s produces unexpected results

[invenia]

Addition/subtraction for some `AnchoredInterval`s produces unexpected results

[omus]

I like that proposal. My only issue is that I think AbstractAnchoredInterval will be used allot and it a little long.

[spurll]

My plan is to proceed with solution 1 for now, and consider 2 in the future.

[omus]

This means that HourEnding{DateTime}(now()) will not be rounded (as it's just an alias for AnchoredInterval{Hour(-1), DateTime}), which may lead to confusion

One way to support HourEnding{DateTime}(now()) to be rounded while having AnchoredInterval{Hour(-1), DateTime}) not be rounded while still using type aliases would be to introduce an additional type parameter.

MWE:

using Base.Dates
using Base.Dates: TimeType
const AbstractDateTime = TimeType

struct AnchoredInterval{P, T, R}
    anchor::T
end

AnchoredInterval{P, T}(i::T) where {P, T} = AnchoredInterval{P, T, false}(i)

const HourEnding{T} = AnchoredInterval{Hour(-1), T, true} where T <: AbstractDateTime
HourEnding{T}(i::T) where T <: AbstractDateTime = invoke(HourEnding{T}, Tuple{Any}, ceil(i, Hour))

HourEnding{DateTime}(now())
AnchoredInterval{Hour(-1), DateTime}(now())

[omus]

I think I would prefer option 2 however.

[spurll]

It seems to me that the third type parameter is likely to cause a lot of confusion.

How do you feel about something like:

AbstractInterval{T} (abstract)
↳ Interval{T} (concrete)
↳ AbstractAnchoredInterval{P, T} (abstract)
  ↳ AnchoredInterval{P, T} (concrete)
  ↳ RoundedAnchoredInterval{P, T} (concrete)
    ↳ HourEnding{T} (type alias for RoundedAnchoredInterval{Hour(-1), T})
    ↳ HourBeginning{T} (type alias for RoundedAnchoredInterval{Hour(1), T})

Names subject to change, of course.