class IO::Handle

Opened file or stream

class IO::Handle { }

Methods

method open

Defined as:

method open(IO::Handle:D:
    :$bin, :$enc, :$chomp, :$nl-in, Str:D :$nl-out,
    Str :$mode,
    :$r, :$w, :$a, :$x, :$update, :$rw, :$rx, :$ra,
    :$create, :$append, :$truncate, :$exclusive,
    --> IO::Handle:D
)

Opens the handle in one of the modes. Fails with appropriate exception if the open fails.

See description of individual methods for the accepted values and behaviour of :$chomp, :$nl-in, :$nl-out, and :$enc. The values for parameters default to the invocant's attributes and if any of them are provided, the attributes will be updated to the new values. Specify :$bin set to True instead of :$enc to indicate the handle should be opened in binary mode. Specifying undefined value as :$enc is equivalent to not specifying :$enc at all. Specifying both a defined encoding as :$enc and :$bin set to true will cause X::IO::BinaryAndEncoding exception to be thrown.

The open mode defaults to non-exclusive, read only (same as specifying :r) and can be controlled by a mix of the following arguments:

:r      same as specifying   :mode<ro>
 
:w      same as specifying   :mode<wo>, :create, :truncate
:a      same as specifying   :mode<wo>, :create, :append
:x      same as specifying   :mode<wo>, :create, :exclusive
 
:update same as specifying   :mode<rw>
:rw     same as specifying   :mode<rw>, :create
:ra     same as specifying   :mode<rw>, :create, :append
:rx     same as specifying   :mode<rw>, :create, :exclusive

Support for combinations of modes other than what is listed above is implementation-dependent and should be assumed unsupported. That is, specifying, for example, .open(:r :create) or .open(:mode<wo> :append :truncate) might work or might cause the Universe to implode, depending on a particular implementation.

The mode details are:

:mode<ro>  means "read only"
:mode<wo>  means "write only"
:mode<rw>  means "read and write"
 
:create    means the file will be created, if it does not exist
:truncate  means the file will be emptied, if it exists
:exclusive means .open will fail if the file already exists
:append    means writes will be done at the end of file's current contents

Attempts to open a directory, write to a handle opened in read-only mode or read from a handle opened in write-only mode, or using text-reading methods on a handle opened in binary mode will fail or throw.

In 6.c language, it's possible to open path '-', which will cause open to open (if closed) the $*IN handle if opening in read-only mode or to open the $*OUT handle if opening in write-only mode. All other modes in this case will result in exception being thrown.

In 6.d language, path '-' has no special meaning.

Note: unlike some other languages, Perl 6 does not use reference counting, and so the file handles are NOT closed when they go out of scope. While they will get closed when garbage collected, garbage collection isn't guaranteed to get run. This means you must use an explicit close on handles opened for writing, to avoid data loss, and an explicit close is recommended on handles opened for reading as well, so that your program does not open too many files at the same time, triggering exceptions on further open calls.

method comb

Defined as:

method comb(IO::Handle:D: Bool :$close, |args --> Seq:D)

Read the handle and processes its contents the same way Str.comb does, taking the same arguments, closing the handle when done if $close is set to a true value. Implementations may slurp the file in its entirety when this method is called.

Attempting to call this method when the handle is in binary mode will result in X::IO::BinaryMode exception being thrown.

my $fh = 'path/to/file'.IO.open;
say "The file has {+$fh.comb: '♥', :close} ♥s in it";

method chomp

Defined as:

has $.chomp is rw = True

One of the attributes that can be set via .new or open. Defaults to True. Takes a Bool specifying whether the line separators (as defined by .nl-in) should be removed from content when using .get or .lines methods.

routine get

Defined as:

method get(IO::Handle:D: --> Str:D)
multi sub get (IO::Handle $fh = $*ARGFILES --> Str:D)

Reads a single line of input from the handle, removing the trailing newline characters (as set by .nl-in) if the handle's .chomp attribute is set to True. Returns Nil, if no more input is available. The subroutine form defaults to $*ARGFILES if no handle is given.

Attempting to call this method when the handle is in binary mode will result in X::IO::BinaryMode exception being thrown.

$*IN.get.say;              # Read one line from the standard input 
 
my $fh = open 'filename';
$fh.get.say;               # Read one line from a file 
$fh.close;
 
say get;                   # Read one line from $*ARGFILES 

routine getc

Defined as:

method getc(IO::Handle:D: --> Str:D)
multi sub getc (IO::Handle $fh = $*ARGFILES --> Str:D)

Reads a single character from the input stream. Attempting to call this method when the handle is in binary mode will result in X::IO::BinaryMode exception being thrown. The subroutine form defaults to $*ARGFILES if no handle is given. Returns Nil, if no more input is available, otherwise operation will block, waiting for at least one character to be available; these caveats apply:

Buffering terminals

Using getc to get a single keypress from a terminal will only work properly if you've set the terminal to "unbuffered". Otherwise the terminal will wait for the return key to be struck or the buffer to be filled up before perl6 gets even a single byte of data.

Waiting for potential combiners

If your handle's encoding allows combining characters to be read, perl6 will wait for more data to be available before it provides a character. This means that inputting an "e" followed by a combining acute will give you an e with an acute rather than giving an "e" and letting the next reading function give you a dangling combiner. However, it also means that when the user inputs just an "e" and has no intention to also input a combining acute, your program will be waiting for another keypress before the initial "e" is returned.

submethod DESTROY

Defined as:

submethod DESTROY(IO::Handle:D:)

Closes the filehandle, unless its native-descriptor is 2 or lower. This ensures the standard file handles do not get inadvertently closed.

Note that garbage collection is not guaranteed to happen, so you must NOT rely on DESTROY for closing the handles you write to and instead close them yourself. Programs that open a lot of files should close the handles explicitly as well, regardless of whether they were open for writing, since too many files might get opened before garbage collection happens and the no longer used handles get closed.

head

method gist

Defined as:

method gist(IO::Handle:D: --> Str:D)

Returns a string containing information which .path, if any, the handle is created for and whether it is .opened.

say IO::Handle.new; # IO::Handle<(Any)>(closed) 
say "foo".IO.open;  # IO::Handle<"foo".IO>(opened) 

method eof

Defined as:

method eof(IO::Handle:D: --> Bool:D)

Returns True if the read operations have exhausted the contents of the handle.

method encoding

Defined as:

multi method encoding(IO::Handle:D: --> Str:D)
multi method encoding(IO::Handle:D: $enc --> Str:D)

Returns a Str representing the encoding currently used by the handle, defaulting to "utf8". Nil indicates the file handle is currently in binary mode. Specifying an optional positional $enc argument switches the encoding used by the handle; specify Nil as encoding to put the handle into binary mode.

The accepted values for encoding are case-insensitive. The available encodings vary by implementation and backend. On Rakudo MoarVM the following are supported:

utf8
utf16
utf8-c8
iso-8859-1
windows-1252
ascii

The default encoding is utf8, which undergoes normalization into Unicode NFC (normalization form canonical). In some cases you may want to ensure no normalization is done; for this you can use utf8-c8. Before using utf8-c8 please read Unicode: File Handles and I/O for more information on utf8-c8 and NFC.

Implementation may choose to also provide support for aliases, e.g. Rakudo allows aliases latin-1 for iso-8859-1 encoding and dashed utf versions: utf-8 and utf-16.

with 'foo'.IO {
    .spurt: "First line is text, then:\nBinary";
    my $fh will leave {.close} = .open;
    $fh.get.say;         # OUTPUT: «First line is text, then:␤» 
    $fh.encoding: Nil;
    $fh.slurp.say;       # OUTPUT: «Buf[uint8]:0x<42 69 6e 61 72 79>␤» 
}

routine lines

Defined as:

sub lines(IO::Handle:D $fh = $*ARGFILES, $limit = Inf, :$close --> Seq:D)
method lines(IO::Handle:D:               $limit = Inf, :$close --> Seq:D)

Return a Seq each element of which is a line from the handle (that is chunks delineated by .nl-in). If the handle's .chomp attribute is set to True, then characters specified by .nl-in will be stripped from each line.

Reads up to $limit lines, where $limit can be a non-negative Int, Inf, or Whatever (which is interpreted to mean Inf). If :$close is set to True, will close the handle when the file ends or $limit is reached. Subroutine form defaults to $*ARGFILES, if no handle is provided.

Attempting to call this method when the handle is in binary mode will result in X::IO::BinaryMode exception being thrown.

NOTE: the lines are read lazily, so ensure the returned Seq is either fully reified or is no longer needed when you close the handle or attempt to use any other methods that change the file position.

say "The file contains ",
  '50GB-file'.IO.open.lines.grep(*.contains: 'Perl').elems,
  " lines that mention Perl";
# OUTPUT: «The file contains 72 lines that mention Perl␤» 

method lock

Defined as:

method lock(IO::Handle:D: Bool:D :$non-blocking = False, Bool:D :$shared = False --> True)

Places an advisory lock on the filehandle. If :$non-blocking is True will fail with X::IO::Lock if lock could not be obtained, otherwise will block until the lock can be placed. If :$shared is True will place a shared (read) lock, otherwise will place an exclusive (write) lock. On success, returns True; fails with X::IO::Lock if lock cannot be placed (e.g. when trying to place a shared lock on a filehandle opened in write mode or trying to place an exclusive lock on a filehandle opened in read mode).

You can use lock again to replace an existing lock with another one. To remove a lock, close the filehandle or use unlock.

# One program writes, the other reads, and thanks to locks either 
# will wait for the other to finish before proceeding to read/write 
 
# Writer 
given "foo".IO.open(:w) {
    .lock;
    .spurt: "I ♥ Perl 6!";
    .close;
}
 
# Reader 
given "foo".IO.open {
    .lock: :shared;
    .slurp.say; # OUTPUT: «I ♥ Perl 6!␤» 
    .close;
}

method unlock

Defined as:

method unlock(IO::Handle:D: --> True)

Removes a lock from the filehandle.

routine words

Defined as:

multi sub words(IO::Handle:D $fh = $*ARGFILES, $limit = Inf, :$close --> Seq:D)
multi method words(IO::Handle:D: $limit = Inf, :$close --> Seq:D)

Similar to Str.words, separates the handle's stream on contiguous chunks of whitespace (as defined by Unicode) and returns a Seq of the resultant "words." Takes an optional $limit argument that can be a non-negative Int, Inf, or Whatever (which is interpreted to mean Inf), to indicate only up-to $limit words must be returned. If Bool :$close named argument is set to True, will automatically close the handle when the returned Seq is exhausted. Subroutine form defaults to $*ARGFILES, if no handle is provided.

Attempting to call this method when the handle is in binary mode will result in X::IO::BinaryMode exception being thrown.

my %dict := bag $*IN.words;
say "Most common words: ", %dict.sort(-*.value).head: 5;

NOTE: implementations may read more data than necessary when a call to .words is made. That is, $handle.words(2) may read more data than two "words" worth of data and subsequent calls to read methods might not read from the place right after the two fetched words. After a call to .words, the file position should be treated as undefined.

method split

Defined as:

method split(IO::Handle:D: :$close, |c)

Slurps the handle's content and calls Str.split on it, forwarding any of the given arguments. If :$close named parameter is set to True, will close the invocant after slurping.

Attempting to call this method when the handle is in binary mode will result in X::IO::BinaryMode exception being thrown.

my $fh = 'path/to/file'.IO.open;
$fh.split: '♥', :close; # Returns file content split on ♥ 

method spurt

Defined as:

multi method spurt(IO::Handle:D: Blob $data, :$close = False)
multi method spurt(IO::Handle:D: Cool $data, :$close = False)

Writes all of the $data into the filehandle, closing it when finished, if $close is True. For Cool $data, will use the encoding the handle is set to use (IO::Handle.open or IO::Handle.encoding).

Behaviour for spurting a Cool when the handle is in binary mode or spurting a Blob when the handle is NOT in binary mode is undefined.

method print

Defined as:

multi method print(**@text --> True)

Writes the given @text to the handle, coercing any non-Str objects to Str by calling .Str method on them. See write to write bytes.

Attempting to call this method when the handle is in binary mode will result in X::IO::BinaryMode exception being thrown.

my $fh = 'path/to/file'.IO.open: :w;
$fh.print: 'some text';
$fh.close;

method print-nl

Defined as:

method print-nl(IO::Handle:D: --> True)

Writes the value of $.nl-out attribute into the handle.

Attempting to call this method when the handle is in binary mode will result in X::IO::BinaryMode exception being thrown.

my $fh = 'path/to/file'.IO.open: :w, :nl-out("\r\n");
$fh.print: "some text";
$fh.print-nl; # prints \r\n 
$fh.close;

method printf

Defined as:

method printf(IO::Handle:D: Cool $format, *@args)

Formats a string based on the given format and arguments and .prints the result into the filehandle. See sub sprintf for details on acceptable format directives.

Attempting to call this method when the handle is in binary mode will result in X::IO::BinaryMode exception being thrown.

my $fh = open 'path/to/file', :w;
$fh.printf: "The value is %d\n", 32;
$fh.close;

method put

Defined as:

multi method put(**@text --> True)

Writes the given @text to the handle, coercing any non-Str objects to Str by calling .Str method on them, and appending the value of .nl-out at the end.

Attempting to call this method when the handle is in binary mode will result in X::IO::BinaryMode exception being thrown.

my $fh = 'path/to/file'.IO.open: :w;
$fh.print: 'some text';
$fh.close;

method say

Defined as:

multi method say(IO::Handle:D: **@text --> True)

This method is identical to put except that it stringifies its arguments by calling .gist instead of .Str.

Attempting to call this method when the handle is in binary mode will result in X::IO::BinaryMode exception being thrown.

my $fh = open 'path/to/file', :w;
$fh.say(Complex.new(3, 4));        # RESULT: «3+4i\n» 
$fh.close;

method read

Defined as:

method read(IO::Handle:D: Int(Cool:D) $bytes = 65536 --> Buf:D)

Binary reading; reads and returns up to $bytes bytes from the filehandle. $bytes defaults to an implementation-specific value (in Rakudo, the value of $*DEFAULT-READ-ELEMS, which by default is set to 65536). This method can be called even when the handle is not in binary mode.

(my $file = 'foo'.IO).spurt: 'I ♥ Perl';
given $file.open {
    say .read: 6; # OUTPUT: «Buf[uint8]:0x<49 20 e2 99 a5 20>␤» 
    .close;
}

method readchars

Defined as:

method readchars(IO::Handle:D: Int(Cool:D) $chars = 65536 --> Str:D)

Reading chars; reads and returns up to $chars chars (graphemes) from the filehandle. $chars defaults to an implementation-specific value (in Rakudo, the value of $*DEFAULT-READ-ELEMS, which by default is set to 65536). Attempting to call this method when the handle is in binary mode will result in X::IO::BinaryMode exception being thrown.

(my $file = 'foo'.IO).spurt: 'I ♥ Perl';
given $file.open {
    say .readchars: 5; # OUTPUT: «I ♥ P␤» 
    .close;
}

method write

Defined as:

method write(IO::Handle:D: Blob:D $buf --> True)

Writes $buf to the filehandle. This method can be called even when the handle is not in binary mode.

method seek

Defined as:

method seek(IO::Handle:D: Int:D $offset, SeekType:D $whence --> True)

Move the file pointer (that is, the position at which any subsequent read or write operations will begin) to the byte position specified by $offset relative to the location specified by $whence which may be one of:

The beginning of the file.

The current position in the file.

The end of the file. Please note that you need to specify a negative offset if you want to position before the end of the file.

method tell

Defined as:

method tell(IO::Handle:D: --> Int:D)

Return the current position of the file pointer in bytes.

method slurp-rest

Defined as:

multi method slurp-rest(IO::Handle:D: :$bin! --> Buf)
multi method slurp-rest(IO::Handle:D: :$enc --> Str)

DEPRECATION NOTICE: this method will be deprecated in 6.d language. Do not use it for new code. Use .slurp method method instead.

Return the remaining content of the file from the current file position (which may have been set by previous reads or by seek.) If the adverb :bin is provided a Buf will be returned, otherwise the return will be a Str with the optional encoding :enc.

method slurp

Defined as:

method slurp(IO::Handle:D: :$close = False)

Returns all the content from the current file position to the end. If the invocant is in binary mode, will return Buf, otherwise will decode the content using invocant's current .encoding and return a Str.

If :$close is set to True, will close the handle when finished reading.

method Supply

Defined as:

multi method Supply(IO::Handle:D: :$size = 65536)

Returns a Supply that will emit the contents of the handle in chunks. The chunks will be Buf if the handle is in binary mode or, if it isn't, Str decoded using same encoding as IO::Handle.encoding.

The size of the chunks is determined by the optional :size named parameter and 65536 bytes in binary mode or 65536 characters in non-binary mode.

"foo".IO.open(:bin).Supply(:size<10>).tap: *.perl.say;
# OUTPUT: 
# Buf[uint8].new(73,32,226,153,165,32,80,101,114,108) 
# Buf[uint8].new(32,54,33,10) 

"foo".IO.open.Supply(:size<10>).tap: *.perl.say; # OUTPUT: # "I ♥ Perl 6" # "!\n"

method path

Defined as:

method path(IO::Handle:D:)

For a handle opened on a file this returns the IO::Path that represents the file. For the standard I/O handles $*IN, $*OUT, and $*ERR it returns an IO::Special object.

method IO

Defined as:

method IO(IO::Handle:D:)

Alias for .path

method Str

Returns the value of .path, coerced to Str.

say "foo".IO.open.path; # OUTPUT: «"foo".IO␤» 

routine close

Defined as:

method close(IO::Handle:D: --> Bool:D)
multi sub close(IO::Handle $fh)

Closes an open file handle. It's not an error to call close on an already-closed filehandle. Returns True on success. If you close one of the standard file handles (by default: $*IN, $*OUT, or $*ERR), that is any handle with native-descriptor 2 or lower, you won't be able to re-open such a handle.

It's a common idiom to use LEAVE phaser for closing the handles, which ensures the handle is closed regardless of how the block is left.

if $do-stuff-with-the-file {
    my $fh = open "path-to-file";
    LEAVE close $fh;
    # ... do stuff with the file 
}
 
sub do-stuff-with-the-file (IO $path-to-file)
  my $fh = $path-to-file.open;
 
  # stick a `try` on it, since this will get run even when the sub is 
  # called with wrong arguments, in which case the `$fh` will be an `Any` 
  LEAVE try close $fh;
 
  # ... do stuff with the file 
}
 
given "foo/bar".IO.open(:w) {
    .spurt: "I ♥ Perl 6!";
    .close;
}

Note: unlike some other languages, Perl 6 does not use reference counting, and so the file handles are NOT closed when they go out of scope. While they will get closed when garbage collected, garbage collection isn't guaranteed to get run. This means you must use an explicit close on handles opened for writing, to avoid data loss, and an explicit close is recommended on handles opened for reading as well, so that your program does not open too many files at the same time, triggering exceptions on further open calls.

Note several methods allow for providing :close argument, to close the handle after the operation invoked by the method completes. As a simpler alternative, the IO::Path type provides many reading and writing methods that let you work with files without dealing with file handles directly.

method flush

Defined as:

method flush(IO::Handle:D: --> True)

Will flush the handle, writing any of the buffered data. Returns True on success; otherwise, fails with X::IO::Flush.

given "foo".IO.open: :w {
    LEAVE .close;
    $fh.print: 'something';
    'foo'.IO.slurp.say; # (if the data got buffered) OUTPUT: «␤» 
    $fh.flush;          # flush the handle 
    'foo'.IO.slurp.say; # OUTPUT: «something␤» 
}

method native-descriptor

Defined as:

method native-descriptor()

This returns a value that the operating system would understand as a "file descriptor" and is suitable for passing to a native function that requires a file descriptor as an argument such as fcntl or ioctl.

method nl-in

Defined as:

method nl-in(--> Str:D) is rw

One of the attributes that can be set via .new or open. Defaults to ["\x0A", "\r\n"]. Takes either a Str or Array of Str specifying input line ending(s) for this handle. If .chomp attribute is set to True, will strip these endings in routines that chomp, such as get and lines.

with 'test'.IO {
    .spurt: '1foo2bar3foo'; # write some data into our test file 
    my $fh will leave {.close} = .open; # can also set .nl-in via .open arg 
    $fh.nl-in = [<foo bar>]; # set two possible line endings to use; 
    $fh.lines.say; # OUTPUT: ("1", "2", "3").Seq 
}

method nl-out

Defined as:

has Str:D $.nl-out is rw = "\n";

One of the attributes that can be set via .new or open. Defaults to "\n". Takes a Str specifying output line ending for this handle, to be used by methods .put and .say.

with 'test'.IO {
    given .open: :w {
        .put: 42;
        .nl-out = 'foo';
        .put: 42;
        .close;
    }
    .slurp.perl.say; # OUTPUT: «"42\n42foo"» 
}

method opened

Defined as:

method opened(IO::Handle:D: --> Bool:D)

Returns True if the handle is open, False otherwise.

method t

Defined as:

method t(IO::Handle:D: --> Bool:D)

Returns True if the handle is opened to a TTY, False otherwise.

Related roles and classes

See also the related role IO and the related class IO::Path.

Type graph

Type relations for IO::Handle
perl6-type-graph IO::Handle IO::Handle Any Any IO::Handle->Any Mu Mu Any->Mu IO::CatHandle IO::CatHandle IO::CatHandle->IO::Handle IO::Pipe IO::Pipe IO::Pipe->IO::Handle IO::ArgFiles IO::ArgFiles IO::ArgFiles->IO::CatHandle

Stand-alone image: vector

Routines supplied by class Any

IO::Handle 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 == (1, 2, 3).one;      # OUTPUT: «True␤» 
say so 1 == (1, 2, 1).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 == (1, 2, 3).none;     # OUTPUT: «False␤» 
say so 4 == (1, 2, 3).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 sub    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 --> List) is 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(&block) is 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 --> List) is 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 [[2, 3], [4, [5, 6]]]».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:D) is 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 ((1, 2), (3), %(:42a));      # OUTPUT: «((1 2) 3 {a => 42})␤» 
say ((1, 2), (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 [[1, 2, 3], [(4, 5), 6, 7]]      .flat; # OUTPUT: «([1 2 3] [(4 5) 6 7])␤» 
say [[1, 2, 3], [(4, 5), 6, 7]]».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:D) is 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:D) is 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:D) is 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:D) is 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 (a => 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 sub item(\x)
multi sub item(|c)
multi sub 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:D) is nodal

Coerce the invocant to Array.

(Any) method List

Defined as:

method List(--> List:D) is nodal

Coerce the invocant to List.

(Any) method Hash

Defined as:

method Hash(--> Hash:D) is nodal

Coerce the invocant to Hash.

(Any) method hash

Defined as:

method hash(--> Hash:D) is nodal

Coerce the invocant to Hash.

(Any) method Slip

Defined as:

method Slip(--> Slip:D) is nodal

Coerce the invocant to Slip.

(Any) method Map

Defined as:

method Map(--> Map:D) is nodal

Coerce the invocant to Map.

(Any) method Bag

Defined as:

method Bag(--> Bag:D) is nodal

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

(Any) method BagHash

Defined as:

method BagHash(--> BagHash:D) is nodal

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

(Any) method Set

Defined as:

method Set(--> Set:D) is nodal

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

(Any) method SetHash

Defined as:

method SetHash(--> SetHash:D) is nodal

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

(Any) method Mix

Defined as:

method Mix(--> Mix:D) is nodal

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

(Any) method MixHash

Defined as:

method MixHash(--> MixHash:D) is nodal

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

(Any) method Supply

Defined as:

method Supply(--> Supply:D) is 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 sum

Defined As:

    method sum(--> TODO)

TODO

(Any) method keys

Defined As:

    method keys(--> TODO)

TODO

(Any) method flatmap

Defined As:

    method flatmap(--> TODO)

TODO

(Any) method roll

Defined As:

    method roll(--> TODO)

TODO

(Any) method pick

Defined As:

    method pick(--> TODO)

TODO

(Any) method head

Defined As:

    method head(--> TODO)

TODO

(Any) method tail

Defined As:

    method tail(--> TODO)

TODO

(Any) method skip

Defined As:

    method skip(--> TODO)

TODO

(Any) method prepend

Defined As:

    method prepend(--> TODO)

TODO

(Any) method unshift

Defined As:

    method unshift(--> TODO)

TODO

(Any) method first

Defined As:

    method first(--> TODO)

TODO

(Any) method unique

Defined As:

    method unique

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

(Any) method repeated

Defined As:

    method repeated(--> TODO)

TODO

(Any) method squish

Defined As:

    method squish(--> TODO)

TODO

(Any) method reduce

Defined As:

    method reduce(--> TODO)

TODO

(Any) method permutations

Defined As:

    method permutations(--> TODO)

TODO

(Any) method categorize

Defined As:

    method categorize(--> TODO)

TODO

(Any) method classify

Defined As:

    method classify(--> TODO)

TODO

(Any) method produce

Defined As:

    method produce(--> TODO)

TODO

(Any) method rotor

Defined As:

    method rotor(--> TODO)

TODO

(Any) method pairs

Defined As:

    method pairs(--> TODO)

TODO

(Any) method antipairs

Defined As:

    method antipairs(--> TODO)

TODO

(Any) method kv

Defined As:

    method kv(--> TODO)

TODO

(Any) method tree

Defined As:

    method tree(--> TODO)

TODO

(Any) method nl-out

Defined As:

    method nl-out(--> TODO)

TODO

(Any) method invert

Defined As:

    method invert(--> TODO)

TODO

(Any) method combinations

Defined As:

    method combinations(--> TODO)

TODO

(Any) method print-nl

Defined As:

    method print-nl(--> TODO)

TODO

(Any) method iterator

Defined As:

    method iterator(--> TODO)

TODO

(Any) method grep

Defined As:

    method grep(--> TODO)

TODO

(Any) method match

Defined As:

    method match(--> TODO)

TODO

(Any) method append

Defined As:

    method append(--> TODO)

TODO

(Any) method join

Defined As:

    method join(--> TODO)

TODO

(Any) method values

Defined As:

    method values(--> TODO)

TODO

(Any) method collate

Defined As:

    method collate(--> TODO)

TODO

(Any) method batch

Defined As:

    method batch(--> TODO)

TODO

(Any) method cache

Defined As:

    method cache(--> TODO)

TODO

Routines supplied by class Mu

IO::Handle 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 [1, 2, 3].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 sub    perl(Mu --> Str)
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. 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, y => 3);
 
say $p;                     # OUTPUT: «Point(2, 3)␤» 
say $p.clone(y => -5);      # OUTPUT: «Point(2, -5)␤» 

(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(-1, 1);

(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 .take, next;
        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(@args) eq '-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(@args) eq '-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(@args) eq '-v' | '-V';
if not $verbose-selected {
    say "Verbose option not present in arguments";
} # OUTPUT: «Verbose option not present in arguments␤»