class Block
class Block is Code { }
A Block is a code object meant for small-scale code reuse. A block is
created syntactically by a list of statements enclosed in curly braces. The literal for
creating an empty block is {;}.
Without an explicit signature or placeholder arguments, a block has $_
as a positional argument, which defaults to the outer scope's $_. Thus it
will inherit the topic if there is any.
my $block = { uc $_; };
say $block.^name; # OUTPUT: «Block»
say $block('hello'); # OUTPUT: «HELLO»
say {;}.signature; # OUTPUT: «(;; $_? is raw = OUTER::<$_>)»
A block can have a Signature between -> or <->
and the block:
my $add = -> $a, $b = 2 { $a + $b };
say $add(40); # OUTPUT: «42»
If the signature is introduced with <->, then the parameters are marked
as rw by default:
|Syntax,<->
my $swap = <-> $a, $b { ($a, $b) = ($b, $a) };
my ($a, $b) = (2, 4);
$swap($a, $b);
say $a; # OUTPUT: «4»
Blocks that aren't of type Routine (which is a subclass of Block) are
transparent to return.
sub f() {
say <a b c>.map: { return 42 };
# ^^^^^^ exits &f, not just the block
}
The last statement is the implicit return value of the block.
say {1}.(); # OUTPUT: «1»
Bare blocks are automatically executed in the order they appear:
say 1; # OUTPUT: «1»
{
say 2; # OUTPUT: «2»; executed directly, not a Block object
}
say 3; # OUTPUT: «3»