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quinnj / Dates.jl

[DEPRECATED] Date/DateTime Implementation for the Julia Language; Successor to Datetime.jl
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Define div or / for Period division? #1

Closed quinnj closed 10 years ago

quinnj commented 10 years ago

Up till now, I've only defined div(::Period,::Period) and left /(::Period,::Period) as a no method error. Mainly to match Base's promotional behavior of / and truncation behavior of div because with the discrete behavior of Dates, we only truncate on division (i.e. Periods are like Integers). I'm wondering if it makes sense to go ahead and define /. Would people be confused if they tried to do Year(1)/Year(2) and got Year(1) as the result?

cc: @StefanKarpinski, @aviks

aviks commented 10 years ago

The typical usecase for division, I'd imagine would be date(x) - date(y)/ year(1). You'd want to multiply the result by something (eg, interest rate), which begs the question of whether the result of the division should be a bare number rather than a period (0.5 or even 1//2 instead of year(1/2))

But in real life, division is not so simple, you need to consider day count conventions (Actual/Actual or 30/365 etc ..). So I wonder if making this an error, rather than giving a naive result is better. cf: https://github.com/aviks/Ito.jl/blob/master/src/time/day_count.jl

In any case, I think / should not promote to div. They ask different questions in the domain: what fraction of of a year is a month vs how many months in a year.

StefanKarpinski commented 10 years ago

I agree with @aviks.

quinnj commented 10 years ago

Sounds good. To be clear, date(x) - date(y)/ year(1), is not allowed because you'd be trying to divide Day/Year. After ditching automatic Period conversions, I haven't figured out a more clean API for specifying a conversion strategy, so that's another issue for another day.