Course of Raku / Advanced / Control flow / Statement prefixes 🆕

sink and quietly

Two more prefixes deal with running code for its effects rather than its value.

The sink prefix evaluates something in sink context — purely for its side effects, discarding the result. It is useful with a lazy operation that you want to force to run:

sink (1..3).map({ print "$_ " });
print "\n"; # 1 2 3

The map here is run only for the printing it does; sink makes sure it actually executes and throws the resulting list away. Without forcing it, a lazy map whose result is never used might not run at all.

The quietly prefix runs a block with its warnings suppressed. Code that would normally print a warning to the error stream stays silent:

my $value;
quietly {
    say $value + 1; # 1, with no "uninitialized value" warning
}

Adding 1 to an undefined $value normally warns about using an uninitialized value, but inside quietly that warning is hidden. Use it when you knowingly do something that warns and do not want the noise — but sparingly, since warnings usually point at a real mistake.

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