See primary documentation in context for infix andthen
andthen operator returns
Empty upon encountering the first undefined argument, otherwise the last argument. Last argument is returned as-is, without being checked for definedness at all. Short-circuits. The result of the left side is bound to
$_ for the right side, or passed as arguments if the right side is a
Callable, whose count must be
A handy use of this operator is to alias a routine's return value to
$_ and to do additional manipulation with it, such as printing or returning it to caller. Since the
andthen operator short-circuits, statements on the right-hand side won't get executed, unless left-hand side is defined (tip: Failures are never defined, so you can handle them with this operator).
sub load-dataload-data.first: /good/ andthen say "$_ is good";# OUTPUT: «(good data is good)␤»load-data() andthen .return; # return loaded data, if it's defineddie "Failed to load data!!";
The above example will print
good data is good only if the subroutine returned any items that match
/good/ and will die unless loading data returned a defined value. The aliasing behavior lets us pipe the values across the operator.
andthen operator is a close relative of the
with statement modifier, and some compilers compile
andthen, meaning these two lines have equivalent behavior:
.say with 42;42 andthen .say;