Why can SAMEPERIODLASTYEAR be used as filter for e.g. CALCULATE?

[DanielM16]

I regularly use SAMEPERIODLASTYEAR with CALCULATE, but I never quite understood why it works. Going by the documentation, SAMEPERIODLASTYEAR appears to return a column of dates. But how is a column of dates a valid input for the <filter> argument of CALCULATE?

CALCULATE(SUM(ResellerSales_USD[SalesAmount_USD]), SAMEPERIODLASTYEAR(DateTime[DateKey]))

Documentation SAMEPERIODLASTYEAR

Documentation CALCULATE

[Singaravelu_R]

SAMEPERIODLASTYEAR() This is a shortcut function that is just a wrapper to DATEADD(). It is 100% equivalent to DATEADD() with “-1, Year” as the last two arguments:

SAMEPERIODLASTYEAR ( Calendar[Date] ) Is exactly the same as: DATEADD ( Calendar[Date], -1, YEAR )

CALCULATE(SUM(ResellerSales_USD[SalesAmount_USD]), SAMEPERIODLASTYEAR(DateTime[DateKey]))=

CALCULATE(SUM(ResellerSales_USD[SalesAmount_USD]), DATEADD ( Calendar[Date], -1, YEAR )))

[DanielM16]

Cool, but how does that answer my question?

[mahoneypat]

All filter expressions in CALCULATE are tables, and SAMEPERIODLASTYEAR (like the other Time Intelligence functions) return a table with a single column of dates.

Regards,

Pat

[DanielM16]

And how does a single column of dates serve as a filter to my original table?

It makes sense that something like this works:

CALCULATE(SUM(tbl[Sales]), tbl[Country]="US")

But I don't understand why the following would work:
CALCULATE(SUM(tbl[Sales]), {2021-04-01, 2021-04-02, 2021-04-03})

(using pseudo code for the second argument to represent a column of dates)