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datesmalltalkpharosqueak

What do the correct arguments for Date dayMonthYearDo: look like in Smalltalk (Pharo / Squeak)

Date dayMonthYearDo: aBlock 
"Supply integers for day, month and year to aBlock and return the result"

^ start dayMonthYearDo: aBlock

What should a typical valid block look like for this message?

Solution

  • In this case the comment "Supply integers, etc." means that the argument aBlock will receive three integers as "actual" arguments: day number, month index and year. This means that you will have to create a block with three "formal" arguments, say, day, monthIndex and year as in:

    aDate dayMonthYearDo: [:day :monthIndex :year | <your code here>]

    The code you write inside <your code here> can refer to the "formal" parameters day, monthIndex and year, much as if it was a method with these three arguments.

    This is how blocks generally work in Smalltalk.

    Example

    aDate
    dayMonthYearDo: [:day :monthIndex :year |
        monthIndex + day = 2
            ifTrue: [Transcript show: 'Happy ' , year asString, '!']]

    UPDATE

    The example above checks for January 1st by "ingeniously" comparing monthIndex + day with 2. In fact, since both variables are >= 1 the only way to get 2 is when day and monthIndex are both 1, i.e., when the receiver aDate is January 1. A more "serious" approach would look like

    (monthIndex = 1 and: [day = 1]) ifTrue: [ <etc> ]