This file was automatically generated from http://svn.pugscode.org/pugs/docs/Perl6/Spec/S32-setting-library/Str.pod on Sat Aug 1 14:01:19 2009 GMT, revision 27701.
DRAFT: Synopsis 32: Setting Library - Str
Rod Adams <rod@rodadams.net>
Larry Wall <larry@wall.org>
Aaron Sherman <ajs@ajs.com>
Mark Stosberg <mark@summersault.com>
Carl Mäsak <cmasak@gmail.com>
Moritz Lenz <moritz@faui2k3.org>
Tim Nelson <wayland@wayland.id.au>
Created: 19 Mar 2009 extracted from S29-functions.pod
Last Modified: 17 Apr 2009
Version: 3
The document is a draft.
If you read the HTML version, it is generated from the pod in the pugs repository under /docs/Perl6/Spec/S32-setting-library/Miscellaneous-scalars.pod so edit it there in the SVN repository if you would like to make changes.
General notes about strings:
A Str can exist at several Unicode levels at once. Which level you
interact with typically depends on what your current lexical context has
declared the "working Unicode level to be". Default is Grapheme.
[Default can't be CharLingua because we don't go into "language"
mode unless there's a specific language declaration saying either
exactly what language we're going into or, in the absence of that, how to
find the exact language somewhere in the enviroment.]
Attempting to use a string at a level higher it can support is handled without warning. The current highest supported level of the string is simply mapped Char for Char to the new higher level. However, attempting to stuff something of a higher level a lower-level string is an error (for example, attempting to store Kanji in a Byte string). An explicit conversion function must be used to tell it how you want it encoded.
Attempting to use a string at a level lower than what it supports is not allowed.
If a function takes a Str and returns a Str, the returned Str
will support the same levels as the input, unless specified otherwise.
The following are all provided by the Str role:
our Char multi method p5chop ( Str $string is rw: ) is export(:P5) my Char multi p5chop ( Str *@strings is rw ) is export(:P5)
Trims the last character from $string, and returns it. Called with a
list, it chops each item in turn, and returns the last character
chopped.
our Str multi method chop ( Str $string: ) is export
Returns string with one Char removed from the end.
our Int multi method p5chomp ( Str $string is rw: ) is export(:P5) my Int multi p5chomp ( Str *@strings is rw ) is export(:P5)
Related to p5chop, only removes trailing chars that match /\n/. In
either case, it returns the number of chars removed.
our Str multi method chomp ( Str $string: ) is export
Returns string with one newline removed from the end. An arbitrary terminator can be removed if the input filehandle has marked the string for where the "newline" begins. (Presumably this is stored as a property of the string.) Otherwise a standard newline is removed.
Note: Most users should just let their I/O handles autochomp instead. (Autochomping is the default.)
our Str multi method lc ( Str $string: ) is export
Returns the input string after converting each character to its lowercase form, if uppercase.
our Str multi method lcfirst ( Str $string: ) is export
Like lc, but only affects the first character.
our Str multi method uc ( Str $string: ) is export
Returns the input string after converting each character to its uppercase form, if lowercase. This is not a Unicode "titlecase" operation, but a full "uppercase".
our Str multi method ucfirst ( Str $string: ) is export
Performs a Unicode "titlecase" operation on the first character of the string.
our Str multi method normalize ( Str $string: Bool :$canonical = Bool::True, Bool :$recompose = Bool::False ) is export
Performs a Unicode "normalization" operation on the string. This involves decomposing the string into its most basic combining elements, and potentially re-composing it. Full detail on the process of decomposing and re-composing strings in a normalized form is covered in the Unicode specification Sections 3.7, Decomposition and 3.11, Canonical Ordering Behavior of the Unicode Standard, 4.0. Additional named parameters are reserved for future Unicode expansion.
For everyday use there are aliases that map to the Unicode Standard Annex #15: Unicode Normalization Forms document's names for the various modes of normalization:
our Str multi method nfd ( Str $string: ) is export {
$string.normalize(:canonical, :!recompose);
}
our Str multi method nfc ( Str $string: ) is export {
$string.normalize(:canonical, :recompose);
}
our Str multi method nfkd ( Str $string: ) is export {
$string.normalize(:!canonical, :!recompose);
}
our Str multi method nfkc ( Str $string: ) is export {
$string.normalize(:!canonical, :recompose);
}
Decomposing a string can be used to compare Unicode strings in a binary form, providing that they use the same encoding. Without decomposing first, two Unicode strings may contain the same text, but not the same byte-for-byte data, even in the same encoding. The decomposition of a string is performed according to tables in the Unicode standard, and should be compatible with decompositions performed by any system.
The :canonical flag controls the use of "compatibility decompositions".
For example, in canonical mode, "ï¬" is left unaffected because it is
not a composition. However, in compatibility mode, it will be replaced
with "fi". Decomposed sequences will be ordered in a canonical way
in either mode.
The :recompose flag controls the re-composition of decomposed forms.
That is, a combining sequence will be re-composed into the canonical
composite where possible.
These de-compositions and re-compositions are performed recursively, until there is no further work to be done.
Note that this function is really only applicable when dealing with codepoint strings. Grapheme strings are normally processed at a higher abstraction level that is independent of normalization, and are lazily normalized into the desired normalization when transferred to lexical scopes or handles that care.
our Str multi method samecase ( Str $string: Str $pattern ) is export
Has the effect of making the case of the string match the case pattern in $pattern.
(Used by s:ii/// internally, see S05.)
our Str multi method sameaccent ( Str $string: Str $pattern ) is export
Has the effect of making the case of the string match the accent pattern in $pattern.
(Used by s:aa/// internally, see S05.)
our Str multi method capitalize ( Str $string: ) is export
Has the effect of first doing an lc on the entire string, then performing a
s:g/(\w+)/{ucfirst $1}/ on it.
our Int multi method chars ( Str $string: ) is export
Returns the number of characters in the string in the current (lexically scoped) idea of what a normal character is, usually graphemes.
our Int multi method codes ( Str $string: ) is export
Returns the number of graphemes in the string in a language-independent way.
our Int multi method codes ( Str $string: $nf = $?NF) is export
Returns the number of codepoints in the string if it were canonicalized the specified way. Do not confuse codepoints with UTF-16 encoding. Characters above U+FFFF count as a single codepoint.
our Int multi method bytes ( Str $string: $enc = $?ENC, :$nf = $?NF) is export
Returns the number of bytes in the string if it were encoded in the specified way. Note the inequality:
.bytes("UTF-16","C") >= .codes("C") * 2
This is caused by the possibility of surrogate pairs, which are counted as one codepoint. However, this problem does not arise for UTF-32:
.bytes("UTF-32","C") == .codes("C") * 4
our Buf multi method encode($encoding = $?ENC, $nf = $?NF)
Returns a Buf which represents the original string in the given encoding
and normal form. The actual return type is as specific as possible, so
$str.encode('UTF-8') returns an utf8 object,
$str.encode('ISO-8859-1') a buf8.
our StrPos multi method index( Str $string: Str $substring, StrPos $pos = StrPos(0) ) is export our StrPos multi method index( Str $string: Str $substring, Int $pos ) is export
index searches for the first occurrence of $substring in $string,
starting at $pos. If $pos is an Int, it is taken to be in the units
of the calling scope, which defaults to "graphemes".
The value returned is always a StrPos object. If the substring
is found, then the StrPos represents the position of the first
character of the substring. If the substring is not found, a bare
StrPos containing no position is returned. This prototype StrPos
evaluates to false because it's really a kind of undef. Do not evaluate
as a number, because instead of returning -1 it will return 0 and issue
a warning.
our Str multi pack( Str::Encoding $encoding, Pair *@items ) our Str multi pack( Str::Encoding $encoding, Str $template, *@items ) our buf8 multi pack( Pair *@items ) our buf8 multi pack( Str $template, *@items )
pack takes a list of pairs and formats the values according to
the specification of the keys. Alternately, it takes a string
$template and formats the rest of its arguments according to
the specifications in the template string. The result is a sequence
of bytes.
An optional $encoding can be used to specify the character
encoding to use in interpreting the result as a Str, otherwise the return
value will simply be a buf containing the bytes generated
by the template(s) and value(s). Note that no guarantee is made
in terms of the final, internal representation of the string, only
that the generated sequence of bytes will be interpreted as a
string in the given encoding, and a string containing those
graphemes will be returned. If the sequence of bytes represents
an invalid string according to $encoding, an exception is generated.
Templates are strings of the form:
grammar Str::PackTemplate {
regex template { [ <group> | <specifier> <count>? ]* }
token group { \( <template> \) }
token specifier { <[aAZbBhHcCsSiIlLnNvVqQjJfdFDpPuUwxX\@]> \!? }
token count { \* |
\[ [ \d+ | <specifier> ] \] |
\d+ }
}
In the pairwise mode, each key must contain a single <group> or
<specifier>, and the values must be either scalar arguments or
arrays.
[ Note: Need more documentation and need to figure out what Perl 5 things no longer make sense. Does Perl 6 need any extra formatting features? -ajs ]
[I think pack formats should be human readable but compiled to an internal form for efficiency. I also think that compact classes should be able to express their serialization in pack form if asked for it with .packformat or some such. -law]
our Str multi method quotemeta ( Str $string: ) is export
Returns the input string with all non-"word" characters back-slashed. That is, all characters not matching "/<[A..Za..z_0..9]>/" will be preceded by a backslash in the returned string, regardless of any locale settings.
[Note from Pm: Should that be "/\w/" instead? Or, if the intent is to duplicate p5 functionality, perhaps it should be "p5quotemeta"? Do we even want this method at all?]
our StrPos multi method rindex( Str $string: Str $substring, StrPos $pos? ) is export our StrPos multi method rindex( Str $string: Str $substring, Int $pos ) is export
Returns the position of the last $substring in $string. If $pos
is specified, then the search starts at that location in $string, and
works backwards. See index for more detail.
our List multi split ( Str $delimiter, Str $input, Int $limit = * ) our List multi split ( Regex $delimiter, Str $input, Int $limit = * ) our List multi method split ( Str $input: Str $delimiter, Int $limit = * ) our List multi method split ( Str $input: Regex $delimiter, Int $limit = *, Bool :$all = False)
Splits a string up into pieces based on delimeters found in the string.
String delimiters must not be treated as rules but as constants. The
default is no longer ' ' since that would be interpreted as a constant.
P5's split(' ') will translate to comb. Null trailing fields
are no longer trimmed by default.
The split function no longer has a default delimiter nor a default invocant.
In general you should use words to split on whitespace now, or comb to break
into individual characters. See below.
If the :all adverb is supplied to the Regex form, then the
delimiters are returned as Match objects in alternation with the
split values. Unlike with Perl 5, if the delimiter contains multiple
captures they are returned as submatches of single Match object.
(And since Match does Capture, whether these Match objects
eventually flatten or not depends on whether the expression is bound
into a list or slice context.)
You may also split lists and filehandles. $*ARGS.split(/\n[\h*\n]+/)
splits on paragraphs, for instance. Lists and filehandles are automatically
fed through cat in order to pretend to be string. The resulting
Cat is lazy. Accessing a filehandle as both a filehandle and as
a Cat is undefined.
our List multi comb ( Regex $matcher, Str $input, Int $limit = * ) our List multi method comb ( Str $input: Regex $matcher = /./, Int $limit = * )
The comb function looks through a string for the interesting bits,
ignoring the parts that don't match. In other words, it's a version
of split where you specify what you want, not what you don't want.
That means the same restrictions apply to the matcher rule as do to split's delimiter rule.
By default it pulls out all individual characters. Saying
$string.comb(/pat/, $n)
is equivalent to
map {.Str}, $string.match(rx:global:x(0..$n):c/pat/)
You may also comb lists and filehandles. +$*IN.comb counts the words on
standard input, for instance. comb(/./, $thing) returns a list of single
Char strings from anything that can give you a Str. Lists and
filehandles are automatically fed through cat in order to pretend to
be string. This Cat is also lazy.
If the :match adverb is applied, a list of Match objects (one
per match) is returned instead of strings. This can be used to
access capturing subrules in the matcher. The unmatched portions
are never returned -- if you want that, use split :all. If the
function is combing a lazy structure, the return values may also be
lazy. (Strings are not lazy, however.)
our List multi words ( Str $input, Int $limit = * ) our List multi method words ( Str $input: Int $limit = * )
Returns a list of non-whitespace bits, i.e. the same as a call to
$input.comb( / \S+ /, $limit ) would.
The flip function reverses a string character by character.
our Str multi method flip ( $str: ) is export {
$str.comb.reverse.join;
}
This function will misplace accents if used at a Unicode level less than graphemes.
our Str multi method sprintf ( Str $format: *@args ) is export
This function is mostly identical to the C library sprintf function.
The $format is scanned for % characters. Any % introduces a
format token. Format tokens have the following grammar:
grammar Str::SprintfFormat {
regex format_token { '%': <index>? <precision>? <modifier>? <directive> }
token index { \d+ '$' }
token precision { <flags>? <vector>? <precision_count> }
token flags { <[ \x20 + 0 \# \- ]>+ }
token precision_count { [ <[1..9]>\d* | '*' ]? [ '.' [ \d* | '*' ] ]? }
token vector { '*'? v }
token modifier { < ll l h m V q L > }
token directive { < % c s d u o x e f g X E G b p n i D U O F > }
}
Directives guide the use (if any) of the arguments. When a directive
(other than %) is used, it indicates how the next argument
passed is to be formatted into the string.
The directives are:
% a literal percent sign c a character with the given codepoint s a string d a signed integer, in decimal u an unsigned integer, in decimal o an unsigned integer, in octal x an unsigned integer, in hexadecimal e a floating-point number, in scientific notation f a floating-point number, in fixed decimal notation g a floating-point number, in %e or %f notation X like x, but using upper-case letters E like e, but using an upper-case "E" G like g, but with an upper-case "E" (if applicable) b an unsigned integer, in binary C special: invokes the arg as code, see below
Compatibility:
i a synonym for %d D a synonym for %ld U a synonym for %lu O a synonym for %lo F a synonym for %f
Perl 5 (non-)compatibility:
n produces a runtime exception (see below) p produces a runtime exception
The special format directive, %C invokes the target argument as
code, passing it the result string that has been generated thus
far and the argument array.
Here's an example of its use:
sprintf "%d%C is %d digits long",
$num,
sub ($s, @args is rw) { @args[2] = $s.elems },
0;
The special directive, %n does not work in Perl 6 because of the
difference in parameter passing conventions, but the example above
simulates its effect using %C.
Modifiers change the meaning of format directives. The most important being support for complex numbers (a basic type in Perl). Here are all of the modifiers and what they modify:
h interpret integer as native "short" (typically int16) l interpret integer as native "long" (typically int32 or int64) ll interpret integer as native "long long" (typically int64) L interpret integer as native "long long" (typically uint64) q interpret integer as native "quads" (typically int64 or larger) m interpret value as a complex number
The m modifier works with d,u,o,x,F,E,G,X,E and G format
directives, and the directive applies to both the real and imaginary
parts of the complex number.
Examples:
sprintf "%ld a big number, %lld a bigger number, %mf complexity\n",
4294967295, 4294967296, 1+2i);
our Str multi method fmt( Scalar $scalar: Str $format = '%s' )
our Str multi method fmt( List $list: Str $format = '%s',
Str $separator = ' ' )
our Str multi method fmt( Hash $hash: Str $format = "%s\t%s",
Str $separator = "\n" )
our Str multi method fmt( Pair $pair: Str $format = "%s\t%s" )
A set of wrappers around sprintf. A call to the scalar version
$o.fmt($format) returns the result of sprintf($format, $o). A call to
the list version @a.fmt($format, $sep) returns the result of
join $sep, map { sprintf($format, $_) }, @a. A call to the hash version
%h.fmt($format, $sep) returns the result of
join $sep, map { sprintf($format, $_.key, $_.value) }, %h.pairs. A call
to the pair version$p.fmt($format) returns the result of
sprintf($format, $p.key, $p.value).
our Str multi method substr (Str $string: StrPos $start, StrLen $length?) is rw is export our Str multi method substr (Str $string: StrPos $start, StrPos $end) is rw is export our Str multi method substr (Str $string: StrPos $start, Int $length) is rw is export our Str multi method substr (Str $string: Int $start, StrLen $length?) is rw is export our Str multi method substr (Str $string: Int $start, StrPos $end) is rw is export our Str multi method substr (Str $string: Int $start, Int $length) is rw is export
substr returns part of an existing string. You control what part by
passing a starting position and optionally either an end position or length.
If you pass a number as either the position or length, then it will be used
as the start or length with the assumtion that you mean "chars" in the
current Unicode abstraction level, which defaults to graphemes. A number
in the 3rd argument is interpreted as a length rather than a position (just
as in Perl 5).
Here is an example of its use:
$initials = substr($first_name,0,1) ~ substr($last_name,0,1);
Optionally, you can use substr on the left hand side of an assignment like so:
$string ~~ /(barney)/; substr($string, $0.from, $0.to) = "fred";
If the replacement string is longer or shorter than the matched sub-string, then the original string will be dynamically resized.
multi method trim() is export;
Returns a copy of the string, with leading and trailing whitespaces removed.
method Match match(Str $self: Regex $search);
See S05/Substitution
method Str subst(Str $self: Regex $search, Str $replacement);
method trans(Str $self: Str $key, Str $val); our multi trans(List of Pair %data);
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