In Operators§
See primary documentation in context for infix andthen
The 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 0
or 1
.
A handy use of this operator is to alias a routine's return value to $_
and to do additional manipulation with it, such as printing or returning it to caller. Since the andthen
operator short-circuits, statements on the right-hand side won't get executed, unless left-hand side is defined (tip: Failure
s are never defined, so you can handle them with this operator).
sub load-dataload-data.first: /good/ andthen say "$_ 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.
The andthen
operator is a close relative of the with
statement modifier, and some compilers compile with
to andthen
, meaning these two lines have equivalent behavior:
.say with 42;42 andthen .say;