class Promise

Status/result of an asynchronous computation

my enum PromiseStatus (:Planned(0), :Kept(1), :Broken(2));
class Promise {}

A Promise is used to handle the result of a computation that might not have finished. It allows the user to execute code once the computation is done (with the then method), execution after a time delay (with in), combining promises, and waiting for results.

my $p = Promise.start({ sleep 242});
$p.then({ say .result });   # will print 42 once the block finished 
say $p.status;              # OUTPUT: «Planned␤» 
$p.result;                  # waits for the computation to finish 
say $p.status;              # OUTPUT: «Kept␤» 

There are two typical scenarios for using promises. The first is to use a factory method (start, in, anyof, allof) on the type object; those will make sure that the promise is automatically kept or broken for you, and you can't call break or keep on these promises yourself.

The second is to create your promises yourself with Promise.new. If you want to ensure that only your code can keep or break the promise, you can use the vow method to get a unique handle, and call keep or break on it:

sub async-get-with-promise($user-agent$url{
    my $p = Promise.new;
    my $v = $p.vow;
 
    # do an asynchronous call on a fictive user agent, 
    # and return the promise: 
    $user-agent.async-get($url,
            on-error => -> $error {
                $v.break($error);
            },
            on-success => -> $response {
                $v.keep($response);
            }
    );
    return $p;
}

Further examples can be found in the concurrency page.

Methods

method start

method start(Promise:U: &code:$scheduler = $*SCHEDULER --> Promise:D)

Creates a new Promise that runs the given code object. The promise will be kept when the code terminates normally, or broken if it throws an exception. The return value or exception can be inspected with the result method.

The scheduler that handles this promise can be passed as a named argument.

There is also a statement prefix start that provides syntactic sugar for this method:

# these two are equivalent: 
my $p1 = Promise.start({ ;#`( do something here ) });
my $p2 = start { ;#`( do something here ) };

method in

method in(Promise:U: $seconds:$scheduler = $*SCHEDULER --> Promise:D)

Creates a new Promise that will be kept in $seconds seconds, or later.

my $proc = Proc::Async.new('perl6''-e''sleep 10; warn "end"');
 
my $result = await Promise.anyof(
    my $promise = $proc.start,
    Promise.in(5).then: { note 'timeout'$proc.kill }
).then: {$promise.result};
# OUTPUT: «timeout␤» 

method at

method at(Promise:U: $at:$scheduler = $*SCHEDULER --> Promise:D)

Creates a new Promise that will be kept at the given time, or later.

my $p = Promise.at(now + 2).then({ say "2 seconds later" });
# do other stuff here 
 
await $p;   # wait here until the 2 seconds are over 

method allof

method allof(Promise:U: *@promises --> Promise:D)

Returns a new promise that will be kept when all the promises passed as arguments are kept or broken. The result of the individual Promises is not reflected in the result of the returned promise: it simply indicates that all the promises have been completed in some way. If the results of the individual promises are important then they should be inspected after the allof promise is kept.

In the following requesting the result of a broken promise will case the original Exception to be thrown. (You may need to run it several times to see the exception.)

my @promises;
for 1..5 -> $t {
    push @promisesstart {
        sleep $t;
    };
}
my $all-done = Promise.allof(@promises);
await $all-done;
@promises>>.result;
say "Promises kept so we get to live another day!";

method anyof

method anyof(Promise:U: *@promises --> Promise:D)

Returns a new promise that will be kept as soon as any of the promises passed as arguments is kept or broken. The result of the completed Promise is not reflected in the result of the returned promise which will always be Kept.

You can use this to wait at most a number of seconds for a promise:

my $timeout = 5;
await Promise.anyof(
    Promise.in($timeout),
    start {
        # do a potentially long-running calculation here 
    },
);

method then

method then(Promise:D: &code)

Schedules a piece of code to be run after the invocant has been kept or broken, and returns a new promise for this computation. In other words, creates a chained promise.

my $timer = Promise.in(2);
my $after = $timer.then({ say "2 seconds are over!"'result' });
say $after.result;  # 2 seconds are over 
                    # result 

method keep

multi method keep(Promise:D:)
multi method keep(Promise:D: \result)

Keeps a promise, optionally setting the result. If no result is passed, the result will be True.

Throws an exception of type X::Promise::Vowed if a vow has already been taken. See method vow for more information.

my $p = Promise.new;
 
if Bool.pick {
    $p.keep;
}
else {
     $p.break;
}

method break

multi method break(Promise:D:)
multi method break(Promise:D: \cause)

Breaks a promise, optionally setting the cause. If no cause is passed, the cause will be False.

Throws an exception of type X::Promise::Vowed if a vow has already been taken. See method vow for more information.

my $p = Promise.new;
 
$p.break('sorry');
say $p.status;          # OUTPUT: «Broken␤» 
say $p.cause;           # OUTPUT: «sorry␤» 

method result

method result(Promise:D)

Waits for the promise to be kept or broken. If it is kept, returns the result; otherwise throws the result as an exception.

method cause

method cause(Promise:D)

If the promise was broken, returns the result (or exception). Otherwise, throws an exception of type X::Promise::CauseOnlyValidOnBroken.

method Bool

multi method Bool(Promise:D:)

Returns True for a kept or broken promise, and False for one in state Planned.

method status

method status(Promise:D --> PromiseStatus)

Returns the current state of the promise: Kept, Broken or Planned:

say "promise got Kept" if $promise.status ~~ Kept;

method scheduler

method scheduler(Promise:D:)

Returns the scheduler that manages the promise.

method vow

my class Vow {
    has Promise $.promise;
    method keep() { ... }
    method break() { ... }
}
method vow(Promise:D: --> Vow:D)

Returns an object that holds the sole authority over keeping or breaking a promise. Calling keep or break on a promise that has vow taken throws an exception of type X::Promise::Vowed.

my $p   = Promise.new;
my $vow = $p.vow;
$vow.keep($p);
say $p.status;          # OUTPUT: «Kept␤» 

method Supply

method Supply(Promise:D:)

Returns a Supply that will emit the result of the Promise being Kept or quit with the cause if the Promise is Broken.

sub await

multi sub await(Promise:D --> Promise)
multi sub await(*@ --> Array)

Waits until one or more promises are all fulfilled, and then returns their values. Also works on channels. Any broken promises will rethrow their exceptions. If a list of promises is provided a list of promises is returned.

Type graph

Type relations for Promise
perl6-type-graph Promise Promise Any Any Promise->Any Mu Mu Any->Mu

Stand-alone image: vector

Routines supplied by class Any

Promise inherits from class Any, which provides the following methods:

(Any) method ACCEPTS

Defined as:

multi method ACCEPTS(Any:D: Mu $other)

Usage:

EXPR.ACCEPTS(EXPR);

Returns True if $other === self (i.e. it checks object identity).

Many built-in types override this for more specific comparisons

(Any) method any

Defined as:

method any(--> Junction:D)

Interprets the invocant as a list and creates an any-Junction from it.

say so 2 == <1 2 3>.any;        # OUTPUT: «True␤» 
say so 5 == <1 2 3>.any;        # OUTPUT: «False␤» 

(Any) method all

Defined as:

method all(--> Junction:D)

Interprets the invocant as a list and creates an all-Junction from it.

say so 1 < <2 3 4>.all;         # OUTPUT: «True␤» 
say so 3 < <2 3 4>.all;         # OUTPUT: «False␤» 

(Any) method one

Defined as:

method one(--> Junction:D)

Interprets the invocant as a list and creates a one-Junction from it.

say so 1 == (123).one;      # OUTPUT: «True␤» 
say so 1 == (121).one;      # OUTPUT: «False␤» 

(Any) method none

Defined as:

method none(--> Junction:D)

Interprets the invocant as a list and creates a none-Junction from it.

say so 1 == (123).none;     # OUTPUT: «False␤» 
say so 4 == (123).none;     # OUTPUT: «True␤» 

(Any) method list

Defined as:

method list(--> List:D)

Interprets the invocant as a list, and returns that List.

say 42.list.^name;           # OUTPUT: «List␤» 
say 42.list.elems;           # OUTPUT: «1␤» 

(Any) method push

Defined as:

method push(|values --> Positional:D)

The method push is defined for undefined invocants and allows for autovivifying undefined to an empty Array, unless the undefined value implements Positional already. The argument provided will then be pushed into the newly created Array.

my %h;
dd %h<a>;      # Any (and therefore undefined) 
%h<a>.push(1); # .push on Any 
dd %h;         # «Hash %h = {:a($[1])}␤» # please note the Array 

(Any) routine reverse

Defined as:

multi        reverse(*@list  --> Seq:D)
multi method reverse(List:D: --> Seq:D)

Returns a Seq with the same elements in reverse order.

Note that reverse always refers to reversing elements of a list; to reverse the characters in a string, use flip.

Examples:

say <hello world!>.reverse;     # OUTPUT: «(world! hello)␤» 
say reverse ^10;                # OUTPUT: «(9 8 7 6 5 4 3 2 1 0)␤» 

(Any) method sort

Defined as:

multi method sort()
multi method sort(&custom-routine-to-use)

Sorts iterables with infix:<cmp> or given code object and returns a new List. Optionally, takes a Callable as a positional parameter, specifying how to sort.

Examples:

say <b c a>.sort;                           # OUTPUT: «(a b c)␤» 
say 'bca'.comb.sort.join;                   # OUTPUT: «abc␤» 
say 'bca'.comb.sort({$^b cmp $^a}).join;    # OUTPUT: «cba␤» 
say '231'.comb.sort(&infix:«<=>»).join;     # OUTPUT: «123␤» 

(Any) method map

Defined as:

multi method map(\SELF: &block;; :$label:$item)
multi method map(HyperIterable:D: &block;; :$label)

map will iterate over the invocant and apply the number of positional parameters of the code object from the invocant per call. The returned values of the code object will become elements of the returned Seq.

The :$label and :$item are useful only internally, since for loops get converted to maps. The :$label takes an existing Label to label the .map's loop with and :$item controls whether the iteration will occur over (SELF,) (if :$item is set) or SELF.

(Any) method deepmap

Defined as:

method deepmap(&block --> Listis nodal

deepmap will apply &block to each element and return a new List with the return values of &block, unless the element does the Iterable role. For those elements deepmap will descend recursively into the sublist.

dd [[1,2,3],[[4,5],6,7]].deepmap(*+1);
# OUTPUT: «[[2, 3, 4], [[5, 6], 7, 8]]␤» 

(Any) method duckmap

Defined as:

method duckmap(&blockis rw is nodal

duckmap will apply &block on each element and return a new list with defined return values of the block. For undefined return values, duckmap will try to descend into the element if that element implements Iterable.

<a b c d e f g>.duckmap(-> $_ where <c d e>.any { .uc }).say;
# OUTPUT: «(a b C D E f g)␤» 
(('d''e'), 'f').duckmap(-> $_ where <e f>.any { .uc }).say;
# OUTPUT: «((d E) F)␤» 

(Any) method nodemap

Defined as:

method nodemap(&block --> Listis nodal

nodemap will apply &block to each element and return a new List with the return values of &block. In contrast to deepmap it will not descend recursively into sublists if it finds elements which does the Iterable role.

say [[1,2,3], [[4,5],6,7], 7].nodemap(*+1);
# OUTPUT: «(4, 4, 8)␤» 
 
say [[23], [4, [56]]]».nodemap(*+1)
# OUTPUT: «((3 4) (5 3))␤» 

The examples above would have produced the exact same results if we had used map instead of nodemap. The difference between the two lies in the fact that map flattens out slips while nodemap doesn't.

say [[2,3], [[4,5],6,7], 7].nodemap({.elems == 1 ?? $_ !! slip});
# OUTPUT: «(() () 7)␤» 
say [[2,3], [[4,5],6,7], 7].map({.elems == 1 ?? $_ !! slip});
# OUTPUT: «(7)␤» 

(Any) method flat

Defined as:

method flat(--> Seq:Dis nodal

Interprets the invocant as a list, flattens non-containerized Iterables into a flat list, and returns that list. Keep in mind Map and Hash types are Iterable and so will be flattened into lists of pairs.

say ((12), (3), %(:42a));      # OUTPUT: «((1 2) 3 {a => 42})␤» 
say ((12), (3), %(:42a)).flat# OUTPUT: «(1 2 3 a => 42)␤» 

Note that Arrays containerize their elements by default, and so flat will not flatten them. You can use hyper method call to call .List method on all the inner Iterables and so de-containerize them, so that flat can flatten them:

say [[123], [(45), 67]]      .flat# OUTPUT: «([1 2 3] [(4 5) 6 7])␤» 
say [[123], [(45), 67]]».List.flat# OUTPUT: «(1 2 3 4 5 6 7)␤» 

For more fine-tuned options, see deepmap, duckmap, and signature destructuring

(Any) method eager

Defined as:

method eager(--> Seq:Dis nodal

Interprets the invocant as a list, evaluates it eagerly, and returns that list.

say (1..10).eager;              # OUTPUT: «(1 2 3 4 5 6 7 8 9 10)␤» 

(Any) method elems

Defined as:

method elems(--> Int:Dis nodal

Interprets the invocant as a list, and returns the number of elements in the list.

say 42.elems;                   # OUTPUT: «1␤» 
say <a b c>.elems;              # OUTPUT: «3␤» 

(Any) method end

method end(--> Any:Dis nodal

Interprets the invocant as a list, and returns the last index of that list.

say 6.end;                      # OUTPUT: «0␤» 
say <a b c>.end;                # OUTPUT: «2␤» 

(Any) method pairup

Defined as:

method pairup(--> Seq:Dis nodal

Interprets the invocant as a list, and constructs a list of pairs from it, in the same way that assignment to a Hash does. That is, it takes two consecutive elements and constructs a pair from them, unless the item in the key position already is a pair (in which case the pair is passed is passed through, and the next list item, if any, is considered to be a key again).

say (=> 1'b''c').pairup.perl;     # OUTPUT: «(:a(1), :b("c")).Seq␤» 

(Any) sub exit

Defined as:

sub exit(Int() $status = 0)

Exits the current process with return code $status.

(Any) sub item

Defined as:

proto sub item(|) is pure
multi item(\x)
multi item(|c)
multi item(Mu $a)

Forces given object to be evaluated in item context and returns the value of it.

say item([1,2,3]).perl;              # OUTPUT: «$[1, 2, 3]␤» 
say item({ apple => 10 }).perl;      # OUTPUT: «${:apple(10)}␤» 
say item("abc").perl;                # OUTPUT: «"abc"␤» 

You can also use $ as item contextualizer.

say $[1,2,3].perl;                   # OUTPUT: «$[1, 2, 3]␤» 
say $("abc").perl;                   # OUTPUT: «"abc"␤» 

(Any) method Array

Defined as:

method Array(--> Array:Dis nodal

Coerce the invocant to Array.

(Any) method List

Defined as:

method List(--> List:Dis nodal

Coerce the invocant to List.

(Any) method Hash

Defined as:

method Hash(--> Hash:Dis nodal

Coerce the invocant to Hash.

(Any) method hash

Defined as:

method hash(--> Hash:Dis nodal

Coerce the invocant to Hash.

(Any) method Slip

Defined as:

method Slip(--> Slip:Dis nodal

Coerce the invocant to Slip.

(Any) method Map

Defined as:

method Map(--> Map:Dis nodal

Coerce the invocant to Map.

(Any) method Bag

Defined as:

method Bag(--> Bag:Dis nodal

Coerce the invocant to Bag, whereby Positionals are treated as lists of values.

(Any) method BagHash

Defined as:

method BagHash(--> BagHash:Dis nodal

Coerce the invocant to BagHash, whereby Positionals are treated as lists of values.

(Any) method Set

Defined as:

method Set(--> Set:Dis nodal

Coerce the invocant to Set, whereby Positionals are treated as lists of values.

(Any) method SetHash

Defined as:

method SetHash(--> SetHash:Dis nodal

Coerce the invocant to SetHash, whereby Positionals are treated as lists of values.

(Any) method Mix

Defined as:

method Mix(--> Mix:Dis nodal

Coerce the invocant to Mix, whereby Positionals are treated as lists of values.

(Any) method MixHash

Defined as:

method MixHash(--> MixHash:Dis nodal

Coerce the invocant to MixHash, whereby Positionals are treated as lists of values.

(Any) method Supply

Defined as:

method Supply(--> Supply:Dis nodal

Coerce the invocant first to a List and then to a Supply.

(Any) method min

Defined As:

multi method min(--> Any:D)
multi method min(&filter --> Any:D)

Coerces to Iterable and returns the numerically smallest element.

If a Callable positional argument is provided, each value is passed into the filter, and its return value is compared instead of the original value. The original value is still the one returned from min.

say (1,7,3).min();       # OUTPUT:«1␤» 
say (1,7,3).min({1/$_}); # OUTPUT:«7␤» 

(Any) method max

Defined As:

multi method max(--> Any:D)
multi method max(&filter --> Any:D)

Coerces to Iterable and returns the numerically largest element.

If a Callable positional argument is provided, each value is passed into the filter, and its return value is compared instead of the original value. The original value is still the one returned from max.

say (1,7,3).max();       # OUTPUT:«7␤» 
say (1,7,3).max({1/$_}); # OUTPUT:«1␤» 

(Any) method minmax

Defined As:

multi method minmax(--> Range:D)
multi method minmax(&filter --> Range:D)

Returns a Range from the smallest to the largest element.

If a Callable positional argument is provided, each value is passed into the filter, and its return value is compared instead of the original value. The original values are still used in the returned Range.

say (1,7,3).minmax();      # OUTPUT:«1..7␤» 
say (1,7,3).minmax({-$_}); # OUTPUT:«7..1␤» 

(Any) method minpairs

Defined As:

multi method minpairs(Any:D: --> Seq:D)

Calls .pairs and returns a Seq with all of the Pairs with minimum values, as judged by the cmp operator:

<a b c a b c>.minpairs.perl.put# OUTPUT: «(0 => "a", 3 => "a").Seq␤» 
%(:42a, :75b).minpairs.perl.put# OUTPUT: «(:a(42),).Seq␤» 

(Any) method maxpairs

Defined As:

multi method maxpairs(Any:D: --> Seq:D)

Calls .pairs and returns a Seq with all of the Pairs with maximum values, as judged by the cmp operator:

<a b c a b c>.maxpairs.perl.put# OUTPUT: «(2 => "c", 5 => "c").Seq␤» 
%(:42a, :75b).maxpairs.perl.put# OUTPUT: «(:b(75),).Seq␤» 

(Any) method keys

Defined As:

multi method keys(Any:U: --> List)
multi method keys(Any:D: --> List)

For defined Any returns its keys, otherwise returns an empty list.

say Any.keys# OUTPUT: «()␤» 

(Any) method flatmap

Defined As:

method flatmap(Any:U: &code --> Seq)

Treats the Any as 1-item list and uses List.flatmap on it.

say Any.flatmap({.reverse}); # OUTPUT: «((Any))␤» 

(Any) method roll

Defined As:

multi method roll(--> Any)
multi method roll($n --> Seq)

Treats the Any as 1-item list and uses List.roll on it.

say Any.roll;    # OUTPUT: «(Any)␤» 
say Any.roll(5); # OUTPUT: «((Any) (Any) (Any) (Any) (Any))␤» 

(Any) method pick

Defined As:

multi method pick(--> Any)
multi method pick($n --> Seq)

Treats the Any as 1-item list and uses List.pick on it.

say Any.pick;    # OUTPUT: «(Any)␤» 
say Any.pick(5); # OUTPUT: «((Any))␤» 

(Any) method skip

Defined As:

multi method skip(--> Seq)
multi method skip($n --> Seq)

Creates a Seq from 1-item list's iterator and uses Seq.skip on it.

say Any.skip;     # OUTPUT: «()␤» 
say Any.skip(5);  # OUTPUT: «()␤» 
say Any.skip(-1); # OUTPUT: «((Any))␤» 

(Any) method prepend

Defined As:

multi method prepend(--> Array)
multi method prepend(@values --> Array)

Initializes Any variable as empty Array and calls Array.prepend on it.

my $a;
say $a.prepend# OUTPUT: «[]␤» 
say $a;         # OUTPUT: «[]␤» 
my $b;
say $b.prepend(1,2,3); # OUTPUT: «[1 2 3]␤» 

(Any) method unshift

Defined As:

multi method unshift(--> Array)
multi method unshift(@values --> Array)

Initializes Any variable as empty Array and calls Array.unshift on it.

my $a;
say $a.unshift# OUTPUT: «[]␤» 
say $a;         # OUTPUT: «[]␤» 
my $b;
say $b.unshift([1,2,3]); # OUTPUT: «[[1 2 3]]␤» 

(Any) method first

Defined As:

method first(Mu $matcher?:$k:$kv:$p:$end)

Treats the Any as a 1-item list and uses List.first on it.

say Any.first# OUTPUT: «(Any)␤» 

(Any) method unique

Defined As:

method unique(:&as:&with --> Seq:D)

Treats the Any as a 1-item list and uses List.unique on it.

say Any.unique# OUTPUT: «((Any))␤» 

(Any) method repeated

Defined As:

method repeated(:&as:&with --> Seq)

Treats the Any as a 1-item list and uses List.repeated on it.

say Any.repeated# OUTPUT: «()␤» 

(Any) method squish

Defined As:

method squish(:&as:&with --> Seq)

Treats the Any as a 1-item list and uses List.squish on it.

say Any.squish# OUTPUT: «((Any))␤» 

(Any) method reduce

Defined As:

method reduce(&with --> Nil)

TODO

(Any) method permutations

Defined As:

method permutations(--> Seq)

Treats the Any as a 1-item list and uses List.permutations on it.

say Any.permutations# OUTPUT: «(((Any)))␤» 

(Any) method categorize

Defined As:

method categorize(&mapper --> Seq)

Treats the Any as a 1-item list and uses List.categorize on it.

say Any.categorize({ $_ }); # OUTPUT: «{(Any) => [(Any)]}␤» 

(Any) method classify

Defined As:

method classify(&mapper --> Seq)

Treats the Any as a 1-item list and uses List.classify on it.

say Any.classify({ $_ }); # OUTPUT: «{(Any) => [(Any)]}␤» 

(Any) method produce

Defined As:

method produce(--> Nil)

TODO

(Any) method pairs

Defined As:

method pairs(--> List)

Returns an empty List.

say Any.pairs# OUTPUT: «()␤» 

(Any) method antipairs

Defined As:

method antipairs(--> List)

Returns an empty List.

say Any.antipairs# OUTPUT: «()␤» 

(Any) method kv

Defined As:

method kv(--> List)

Returns an empty List.

say Any.kv# OUTPUT: «()␤» 

(Any) method tree

Defined As:

method tree(--> Any)

Returns Any.

say Any.tree# OUTPUT: «Any␤» 

(Any) method nl-out

Defined As:

method nl-out(--> Str)

Returns Str with the value of "\n". See IO::Handle.nl-out for the details.

say Any.nl-out# OUTPUT: «␤␤» 

(Any) method invert

Defined As:

method invert(--> List)

Returns an empty List.

say Any.invert# OUTPUT: «()␤» 

(Any) method combinations

Defined As:

method combinations(--> Seq)

Treats the Any as a 1-item list and uses List.combinations on it.

say Any.combinations# OUTPUT: «(() ((Any)))␤» 

(Any) method iterator

Defined As:

method iterator(--> Iterator)

Treats the Any as 1-item list and uses iterator on it.

my $it = Any.iterator;
say $it.pull-one# OUTPUT: «(Any)␤» 
say $it.pull-one# OUTPUT: «IterationEnd␤» 

(Any) method grep

Defined As:

method grep(Mu $matcher:$k:$kv:$p:$v --> Seq)

Treats the Any as 1-item list and uses List.grep on it.

Based on $matcher value can be either ((Any)) or empty List.

my $a;
say $a.grep({ True }); # OUTPUT: «((Any))␤» 
say $a.grep({ $_ });   # OUTPUT: «()␤» 

(Any) method append

Defined As:

method append(@values --> Array)

Initializes Any variable as empty Array and calls Array.append on it.

my $a;
say $a.append# OUTPUT: «[]␤» 
my $b;
say $b.append((1,2,3)); # OUTPUT: «[1 2 3]␤» 

(Any) method values

Defined As:

method values(--> List)

Returns an empty List.

(Any) method collate

Defined As:

method collate(--> Seq)

TODO

(Any) method cache

Defined As:

method cache(--> List)

TODO

Routines supplied by class Mu

Promise inherits from class Mu, which provides the following methods:

(Mu) routine defined

multi sub    defined(Mu --> Bool:D)
multi method defined(   --> Bool:D)

Returns False on the type object, and True otherwise.

say Int.defined;                # OUTPUT: «False␤» 
say 42.defined;                 # OUTPUT: «True␤» 

Very few types (like Failure) override defined to return False even for instances:

sub fails() { fail 'oh noe' };
say fails().defined;            # OUTPUT: «False␤» 

(Mu) routine isa

multi method isa(Mu $type     --> Bool:D)
multi method isa(Str:D $type  --> Bool:D)

Returns True if the invocant is an instance of class $type, a subset type or a derived class (through inheritance) of $type.

my $i = 17;
say $i.isa("Int");   # OUTPUT: «True␤» 
say $i.isa(Any);     # OUTPUT: «True␤» 

A more idiomatic way to do this is to use the smartmatch operator ~~ instead.

my $s = "String";
say $s ~~ Str;       # OUTPUT: «True␤» 

(Mu) routine does

method does(Mu $type --> Bool:D)

Returns True if and only if the invocant conforms to type $type.

my $d = Date.new('2016-06-03');
say $d.does(Dateish);             # True    (Date does role Dateish) 
say $d.does(Any);                 # True    (Date is a subclass of Any) 
say $d.does(DateTime);            # False   (Date is not a subclass of DateTime) 

Using the smart match operator ~~ is a more idiomatic alternative.

my $d = Date.new('2016-06-03');
say $d ~~ Dateish;                # OUTPUT: «True␤» 
say $d ~~ Any;                    # OUTPUT: «True␤» 
say $d ~~ DateTime;               # OUTPUT: «False␤» 

(Mu) routine Bool

multi sub    Bool(Mu --> Bool:D)
multi method Bool(   --> Bool:D)

Returns False on the type object, and True otherwise.

Many built-in types override this to be False for empty collections, the empty string or numerical zeros

say Mu.Bool;                    # OUTPUT: «False␤» 
say Mu.new.Bool;                # OUTPUT: «True␤» 
say [123].Bool;             # OUTPUT: «True␤» 
say [].Bool;                    # OUTPUT: «False␤» 
say { 'hash' => 'full' }.Bool;  # OUTPUT: «True␤» 
say {}.Bool;                    # OUTPUT: «False␤» 
say "".Bool;                    # OUTPUT: «False␤» 
say 0.Bool;                     # OUTPUT: «False␤» 
say 1.Bool;                     # OUTPUT: «True␤» 
say "0".Bool;                   # OUTPUT: «True␤» 

(Mu) method Capture

Defined as:

method Capture(Mu:D: --> Capture:D)

Returns a Capture with named arguments corresponding to invocant's public attributes:

class Foo {
    has $.foo = 42;
    has $.bar = 70;
    method bar { 'something else' }
}.new.Capture.say# OUTPUT: «\(:bar("something else"), :foo(42))␤» 

(Mu) method Str

multi method Str(--> Str)

Returns a string representation of the invocant, intended to be machine readable. Method Str warns on type objects, and produces the empty string.

say Mu.Str;                     # Use of uninitialized value of type Mu in string context. 

(Mu) routine gist

multi sub    gist(+args --> Str)
multi method gist(   --> Str)

Returns a string representation of the invocant, optimized for fast recognition by humans. As such lists will be truncated at 100 elements. Use .perl to get all elements.

The default gist method in Mu re-dispatches to the perl method for defined invocants, and returns the type name in parenthesis for type object invocants. Many built-in classes override the case of instances to something more specific that may truncate output.

gist is the method that say calls implicitly, for non-Str types, so say $something and say $something.gist generally produce the same output.

say Mu.gist;        # OUTPUT: «(Mu)␤» 
say Mu.new.gist;    # OUTPUT: «Mu.new␤» 

(Mu) routine perl

multi method perl(--> Str)

Returns a Perlish representation of the object (i.e., can usually be re-evaluated with EVAL to regenerate the object). The exact output of perl is implementation specific, since there are generally many ways to write a Perl expression that produces a particular value

(Mu) method item

method item(Mu \item:is raw

Forces the invocant to be evaluated in item context and returns the value of it.

say [1,2,3].item.perl;         # OUTPUT: «$[1, 2, 3]␤» 
say { apple => 10 }.item.perl# OUTPUT: «${:apple(10)}␤» 
say "abc".item.perl;           # OUTPUT: «"abc"␤» 

(Mu) method self

method self(--> Mu)

Returns the object it is called on.

(Mu) method clone

method clone(*%twiddles)

Creates a shallow clone of the invocant, including shallow cloning of private attributes. Alternative values for public attributes can be provided via named arguments with names matching the attributes' names.

class Point2D {
    has ($.x$.y);
    multi method gist(Point2D:D:{
        "Point($.x$.y)";
    }
}
 
my $p = Point2D.new(x => 2=> 3);
 
say $p;                     # OUTPUT: «Point(2, 3)␤» 
say $p.clone(=> -5);      # OUTPUT: «Point(2, -5)␤» 

Note that .clone does not go the extra mile to shallow-copy @. and %. sigiled attributes and, if modified, the modifications will still be available in the original object:

class Foo {
    has $.foo is rw = 42;
    has &.boo is rw = { say "Hi" };
    has @.bar       = <a b>;
    has %.baz       = <a b c d>;
}
 
my $o1 = Foo.new;
with my $o2 = $o1.clone {
    .foo = 70;
    .bar = <Z Y>;
    .baz = <Z Y X W>;
    .boo = { say "Bye" };
}
 
# Hash and Array attribute modifications in clone appear in original as well: 
say $o1;    # OUTPUT: «Foo.new(foo => 42, bar => ["Z", "Y"], baz => {:X("W"), :Z("Y")}, …␤» 
say $o2;    # OUTPUT: «Foo.new(foo => 70, bar => ["Z", "Y"], baz => {:X("W"), :Z("Y")}, …␤» 
$o1.boo.(); # OUTPUT: «Hi␤» 
$o2.boo.(); # OUTPUT: «Bye␤» 

To clone those, you could implement your own .clone that clones the appropriate attributes and passes the new values to Mu.clone, for example, via nextwith. Alternatively, your own .clone could clone self first (using self.Mu::clone or callsame) and then manipulate the clone as needed, before returning it.

class Bar {
    has @.foo = <a b>;
    has %.bar = <a b c d>;
    method clone { nextwith :foo(@!foo.clone:bar(%!bar.clone}
}
 
my $o1 = Bar.new;
with my $o2 = $o1.clone {
    .foo = <Z Y>;
    .bar = <Z Y X W>;
}
 
# Hash and Array attribute modifications in clone do not affect original: 
say $o1# OUTPUT: «Bar.new(foo => ["a", "b"], bar => {:a("b"), :c("d")})␤» 
say $o2# OUTPUT: «Bar.new(foo => ["Z", "Y"], bar => {:X("W"), :Z("Y")})␤» 

(Mu) method new

multi method new(*%attrinit)

Default method for constructing (create + initialize) new objects of a class. This method expects only named arguments which are then used to initialize attributes with accessors of the same name.

Classes may provide their own new method to override this default.

new triggers an object construction mechanism that calls submethods named BUILD in each class of an inheritance hierarchy, if they exist. See the documentation on object construction for more information.

(Mu) method bless

method bless(*%attrinit --> Mu:D)

Lower-level object construction method than new.

Creates a new object of the same type as the invocant, uses the named arguments to initialize attributes, and returns the created object.

You can use this method when writing custom constructors:

class Point {
    has $.x;
    has $.y;
    multi method new($x$y{
        self.bless(:$x:$y);
    }
}
my $p = Point.new(-11);

(Though each time you write a custom constructor, remember that it makes subclassing harder).

(Mu) method CREATE

method CREATE(--> Mu:D)

Allocates a new object of the same type as the invocant, without initializing any attributes.

say Mu.CREATE.defined;  # OUTPUT: «True␤» 

(Mu) method print

multi method print(--> Bool:D)

Prints value to $*OUT after stringification using .Str method without adding a newline at end.

"abc\n".print;          # RESULT: «abc␤» 

(Mu) method put

multi method put(--> Bool:D)

Prints value to $*OUT, adding a newline at end, and if necessary, stringifying non-Str object using the .Str method.

"abc".put;              # RESULT: «abc␤» 

(Mu) method say

multi method say(--> Bool:D)

Prints value to $*OUT after stringification using .gist method with newline at end. To produce machine readable output use .put.

say 42;                 # OUTPUT: «42␤» 

(Mu) method ACCEPTS

multi method ACCEPTS(Mu:U: $other)

ACCEPTS is the method that smart matching with the infix ~~ operator and given/when invokes on the right-hand side (the matcher).

The Mu:U multi performs a type check. Returns True if $other conforms to the invocant (which is always a type object or failure).

say 42 ~~ Mu;           # OUTPUT: «True␤» 
say 42 ~~ Int;          # OUTPUT: «True␤» 
say 42 ~~ Str;          # OUTPUT: «False␤» 

Note that there is no multi for defined invocants; this is to allow autothreading of junctions, which happens as a fallback mechanism when no direct candidate is available to dispatch to.

(Mu) method WHICH

multi method WHICH(--> ObjAt:D)

Returns an object of type ObjAt which uniquely identifies the object. Value types override this method which makes sure that two equivalent objects return the same return value from WHICH.

say 42.WHICH eq 42.WHICH;       # OUTPUT: «True␤» 

(Mu) method WHERE

method WHERE(--> Int)

Returns an Int representing the memory address of the object.

(Mu) method WHY

multi method WHY()

Returns the attached Pod value. For instance,

sub cast(Spell $s)
#= Initiate a specified spell normally 
#= (do not use for class 7 spells) 
{
do-raw-magic($s);
}
say &cast.WHY;
# OUTPUT: «Initiate a specified spell normally (do not use for class 7 spells)␤» 

See the documentation specification for details about attaching Pod to variables, classes, functions, methods, etc.

(Mu) trait is export

multi sub trait_mod:<is>(Mu:U \type:$export!)

Marks a type as being exported, that is, available to external users.

my class SomeClass is export { }

A user of a module or class automatically gets all the symbols imported that are marked as is export.

See Exporting and Selective Importing Modules for more details.

(Mu) method return

method return()

The method return will stop execution of a subroutine or method, run all relevant phasers and provide invocant as a return value to the caller. If a return type constraint is provided it will be checked unless the return value is Nil. A control exception is raised and can be caught with CONTROL.

sub f { (1|2|3).return };
dd f(); # OUTPUT: «any(1, 2, 3)␤» 

(Mu) method return-rw

Same as method return except that return-rw returns a writable container to the invocant (see more details here: return-rw).

(Mu) method emit

method emit()

Emits the invocant into the enclosing supply or react block.

react { whenever supply { .emit for "foo"42.5 } {
    say "received {.^name} ($_)";
}}
 
# OUTPUT: 
# received Str (foo) 
# received Int (42) 
# received Rat (0.5) 

(Mu) method take

method take()

Returns the invocant in the enclosing gather block.

sub insert($sep+@list{
    gather for @list {
        FIRST .takenext;
        take slip $sep.item
    }
}
 
say insert ':', <a b c>;
# OUTPUT: «(a : b : c)␤» 

(Mu) routine take

sub take(\item)

Takes the given item and passes it to the enclosing gather block.

#| randomly select numbers for lotto 
my $num-selected-numbers = 6;
my $max-lotto-numbers = 49;
gather for ^$num-selected-numbers {
    take (1 .. $max-lotto-numbers).pick(1);
}.say;    # six random values 

(Mu) routine take-rw

sub take-rw(\item)

Returns the given item to the enclosing gather block, without introducing a new container.

my @a = 1...3;
sub f(@list){ gather for @list { take-rw $_ } };
for f(@a{ $_++ };
say @a;
# OUTPUT: «[2 3 4]␤» 

(Mu) method so

method so()

Returns a Bool value representing the logical non-negation of an expression. One can use this method similarly to the English sentence: "If that is so, then do this thing". For instance,

my @args = <-a -e -b -v>;
my $verbose-selected = any(@argseq '-v' | '-V';
if $verbose-selected.so {
    say "Verbose option detected in arguments";
} # OUTPUT: «Verbose option detected in arguments␤» 

(Mu) method not

method not()

Returns a Bool value representing the logical negation of an expression. Thus it is the opposite of so.

my @args = <-a -e -b>;
my $verbose-selected = any(@argseq '-v' | '-V';
if $verbose-selected.not {
    say "Verbose option not present in arguments";
} # OUTPUT: «Verbose option not present in arguments␤» 

Since there is also a prefix version of not, the above code reads better like so:

my @args = <-a -e -b>;
my $verbose-selected = any(@argseq '-v' | '-V';
if not $verbose-selected {
    say "Verbose option not present in arguments";
} # OUTPUT: «Verbose option not present in arguments␤»