class Block

Code object with its own lexical scope

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.

Without an explicit signature or placeholder arguments, a block has $_ as a positional argument

my $block = { uc $_};
say $block.^name;           # OUTPUT: «Block␤» 
say $block('hello');        # OUTPUT: «HELLO␤» 

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:

my $swap = <-> $a$b { ($a$b= ($b$a};
my ($a$b= (24);
$swap($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 in sink context are automatically executed:

say 1;
{
    say 2;                  # executed directly, not a Block object 
}
say 3;

Type Graph

Type relations for Block
perl6-type-graph Block Block Code Code Block->Code Mu Mu Any Any Any->Mu Callable Callable Code->Any Code->Callable Routine Routine Routine->Block Macro Macro Macro->Routine Sub Sub Sub->Routine Method Method Method->Routine Submethod Submethod Submethod->Routine Regex Regex Regex->Method

Stand-alone image: vector

Routines supplied by class Code

Block inherits from class Code, which provides the following routines:

(Code) method ACCEPTS

multi method ACCEPTS(Code:D: Mu $topic)

Usually calls the code object and passes $topic as an argument. However, when called on a code object that takes no arguments, the code object is invoked with no arguments and $topic is dropped. The result of the call is returned.

(Code) method arity

Defined as:

method arity(Code:D: --> Int:D)

Returns the minimum number of positional arguments that must be passed in order to call the code object. Any optional or slurpy parameters in the code object's Signature do not contribute, nor do named parameters.

sub argless() { }
sub args($a$b?{ }
sub slurpy($a$b*@c{ }
say &argless.arity;             # OUTPUT: «0␤» 
say &args.arity;                # OUTPUT: «1␤» 
say &slurpy.arity;              # OUTPUT: «2␤» 

(Code) method assuming

method assuming(Callable:D $self: |primers)

Returns a Callable that implements the same behaviour as the original, but has the values passed to .assuming already bound to the corresponding parameters.

my sub slow($n){ my $i = 0$i++ while $i < $n$i };
 
# takes only one parameter and as such wont forward $n 
sub bench(&c){ cnow - ENTER now };
 
say &slow.assuming(10000000).&bench# OUTPUT: «(10000000 7.5508834)␤» 

For a sub with arity greater than one, you can use Whatever * for all of the positional parameters that are not "assumed".

sub first-and-last ( $first$last ) {
    say "Name is $first $last";
}
 
my &surname-smith = &first-and-last.assuming*'Smith' );
 
&surname-smith.'Joe' ); # OUTPUT: «Name is Joe Smith␤» 

You can handle any combination of assumed and not assumed positional parameters:

sub longer-names ( $first$middle$last$suffix ) {
    say "Name is $first $middle $last $suffix";
}
 
my &surname-public = &longer-names.assuming**'Public'* );
 
&surname-public.'Joe''Q.''Jr.'); # OUTPUT: «Name is Joe Q. Public Jr.␤» 

Named parameters can be assumed as well:

sub foo { say "$^a $^b $:foo $:bar" }
&foo.assuming(13:42foo)(24:72bar); # OUTPUT: «13 24 42 72␤» 

And you can use .assuming on all types of Callables, including Methods and Blocks:

# We use a Whatever star for the invocant: 
my &comber = Str.^lookup('comb').assuming: *, /\w+/;
say comber 'Perl is awesome! Python is great! And PHP is OK too';
# OUTPUT: «(Perl Python PHP)␤» 
 
my &learner = {
    "It took me $:months months to learn $^lang"
}.assuming: 'Perl 6';
say learner :6months;  # OUTPUT: «It took me 6 months to learn Perl 6␤» 

(Code) method count

Defined as:

method count(Code:D: --> Real:D)

Returns the maximum number of positional arguments that may be passed when calling the code object. For code objects that can accept any number of positional arguments (that is, they have a slurpy parameter), count will return Inf. Named parameters do not contribute.

sub argless() { }
sub args($a$b?{ }
sub slurpy($a$b*@c{ }
say &argless.count;             # OUTPUT: «0␤» 
say &args.count;                # OUTPUT: «2␤» 
say &slurpy.count;              # OUTPUT: «Inf␤» 

(Code) method signature

Defined as:

multi method signature(Code:D: --> Signature:D)

Returns the Signature object for this code object, which describes its parameters.

sub a(Int $oneStr $two{};
say &a.signature# OUTPUT: «(Int $one, Str $two)␤» 

(Code) method Str

Defined as:

multi method Str(Code:D: --> Str:D)

Will produce a warning. Use .perl or .gist instead.

sub marine() { }
say ~&marine;    # OUTPUT: «marine␤» 
say &marine.Str# OUTPUT: «marine␤» 

(Code) method file

Defined as:

method file(Code:D: --> Str:D)

Returns the name of the file in which the code object was declared.

say &infix:<+>.file;

(Code) method line

Defined as

method line(Code:D: --> Int:D)

Returns the line number in which the code object was declared.

say &infix:<+>.line;

Routines supplied by role Callable

Block inherits from class Code, which does role Callable, which provides the following routines:

(Callable) method CALL-ME

method CALL-ME(Callable:D $self: |arguments)

This method is required for postfix:«( )» and postfix:«.( )». It's what makes an object actually call-able and needs to be overloaded to let a given object act like a routine. If the object needs to be stored in a &-sigiled container, is has to implement Callable.

class A does Callable {
    submethod CALL-ME(|c){ 'called' }
}
my &a = A;
say a(); # OUTPUT: «called␤» 

(Callable) method Capture

Defined as:

method Capture()

Throws X::Cannot::Capture.