Course of Raku / Advanced / Subroutines / Anonymous subroutines / Exercises / Triple it

Solution: Triple it

Here is a possible solution to the task.

Code

my $factor = 3;
my $scale = -> $x { $x * $factor };

say $scale(7);

🦋 You can find the source code in the file triple-it.raku.

Output

21

Comments

1. The pointy block uses $factor, a variable from the surrounding scope, even though it is only a parameter $x short. Capturing such variables is what makes it a closure.

2. With $factor equal to 3, calling $scale(7) gives 21. Change $factor and the same block would scale by the new value:

$factor = 5;
say $scale(7); # 35

Because the closure captures the variable rather than its value at the time it was written, the later call sees the updated $factor and returns 35.

Course navigation

← Triple it   |   An anonymous square →