> On 21 Nov 2017, at 18:07, Alistair Grant <akgrant0...@gmail.com> wrote: > > On 20 November 2017 at 09:16, Sven Van Caekenberghe <s...@stfx.eu> wrote: >> >> We can discuss about this ad infinitum. I think we all agree that >> there are 2 views (abstract calendar date and concrete time >> interval/span, which requires a TZ), as well as 2 possible ways to >> deal with the second case (TZ inside date or as context outside of the >> date). > > > Right, I think changing things now will be quite a bit of work. > > However there are a couple of things we can do to make life a bit easier: > > 1. Add a method that facilitates TZ independent comparisons. > 2. Add a bit more information in the class comments. > > > I've named the method #dmyEquals: below, although I don't particularly > like it. If anyone has a better idea, please reply.
#equals: #calendarEquals: #equalIgnoreTimezone: > I've also added some proposed text for the class comments. More comments are always good. > If I don't hear back in a couple of days I'll submit a PR (with > automated tests). > > > Cheers, > Alistair > > ---- > > dmyEquals: aDate > "Perform a time zone independent comparison of the dates, i.e. > only compare day, month and year" > > ^self year = aDate year and: [ > self monthIndex = aDate monthIndex and: > [ self dayOfMonth = aDate dayOfMonth ] ] > > ---- > Class comment: > > Instances of Date are Timespans with duration of 1 day. > Their default creation assumes a start of midnight in the local time zone. > > !Comparing Dates > > We tend to use dates in one of two modes: > > - Time zone dependent > - Time zone independent > > In the first instance, dates are only the same if they are in the same > time zone (otherwise they are two different 24 hour periods). This is > the default behaviour of Date. > > In the second, comparison is only interested in whether the day, month > and year are the same. > > As an example, take someone's birthday. If I want to know whether we > were born on the same day, I will want to compare dates without time > zones. If I want to know if it is currently their birthday where they > are, I'll want to use time zones. > > > [[[language=smalltalk > | birthday1 birthday2 | > > birthday1 := (DateAndTime fromString: '2018/01/01T00:00:00+10') asDate. > birthday2 := (DateAndTime fromString: '2018/01/01T00:00:00+01') asDate. > > "Is it person 1's birthday now? (where they live: UTC+10)" > birthday1 includes: DateAndTime now. > > "Do person 1 and person 2 have the same birthday?" > birthday1 dmyEquals: birthday2. > ]]] >
