How do I extract the components of a tuple in DAML?

问题

Given a pair in DAML, e.g. constructed by (1, "test"), how can I get the first and second components out?

回答1:

Given a DAML pair x of type (Int, Text), you can get the first component (1 in your example) using the selector x._1 or the fst function as fst x. You can get the second component ("test" in your example) with x._2 or snd x.

The x._1 selector works on all tuples (pairs, triples and beyond), while fst only works on pairs. The function fst3 (and snd3, thd3) are available in DA.Tuple to work on triples.

回答2:

For a tuple that has a number of elements, you could use

let (a,_,c,_) = someFunction

-- do something to a or c

来源：https://stackoverflow.com/questions/53763514/how-do-i-extract-the-components-of-a-tuple-in-daml