NAME
String::Tagged - string buffers with value tags on extents
SYNOPSIS
use String::Tagged;
my $st = String::Tagged->new( "An important message" );
$st->apply_tag( 3, 9, bold => 1 );
$st->iter_substr_nooverlap(
sub {
my ( $substring, %tags ) = @_;
print $tags{bold} ? "$substring"
: $substring;
}
);
DESCRIPTION
This module implements an object class, instances of which store a
(mutable) string buffer that supports tags. A tag is a name/value pair
that applies to some extent of the underlying string.
The types of tag names ought to be strings, or at least values that are
well-behaved as strings, as the names will often be used as the keys in
hashes or applied to the eq operator.
The types of tag values are not restricted - any scalar will do. This
could be a simple integer or string, ARRAY or HASH reference, or even a
CODE reference containing an event handler of some kind.
Tags may be arbitrarily overlapped. Any given offset within the string
has in effect, a set of uniquely named tags. Tags of different names
are independent. For tags of the same name, only the latest, shortest
tag takes effect.
For example, consider a string with three tags represented here:
Here is my string with tags
[-------------------------] foo => 1
[-------] foo => 2
[---] bar => 3
Every character in this string has a tag named foo. The value of this
tag is 2 for the words my and string and the space inbetween, and 1
elsewhere. Additionally, the words is and my and the space between them
also have the tag bar with a value 3.
Since String::Tagged does not understand the significance of the tag
values it therefore cannot detect if two neighbouring tags really
contain the same semantic idea. Consider the following string:
A string with words
[-------] type => "message"
[--------] type => "message"
This string contains two tags. String::Tagged will treat this as two
different tag values as far as iter_tags_nooverlap is concerned, even
though get_tag_at yields the same value for the type tag at any
position in the string. The merge_tags method may be used to merge tag
extents of tags that should be considered as equal.
NAMING
I spent a lot of time considering the name for this module. It seems
that a number of people across a number of languages all created
similar functionality, though named very differently. For the benefit
of keyword-based search tools and similar, here's a list of some other
names this sort of object might be known by:
* Extents
* Overlays
* Attribute or attributed strings
* Markup
* Out-of-band data
CONSTRUCTOR
new
$st = String::Tagged->new( $str )
Returns a new instance of a String::Tagged object. It will contain no
tags. If the optional $str argument is supplied, the string buffer will
be initialised from this value.
If $str is a String::Tagged object then it will be cloned, as if
calling the clone method on it.
new_tagged
$st = String::Tagged->new_tagged( $str, %tags )
Shortcut for creating a new String::Tagged object with the given tags
applied to the entire length. The tags will not be anchored at either
end.
clone (class)
$new = String::Tagged->clone( $orig, %opts )
Returns a new instance of String::Tagged made by cloning the original,
subject to the options provided. The returned instance will be in the
requested class, which need not match the class of the original.
The following options are recognised:
only_tags => ARRAY
If present, gives an ARRAY reference containing tag names. Only those
tags named here will be copied; others will be ignored.
except_tags => ARRAY
If present, gives an ARRAY reference containing tag names. All tags
will be copied except those named here.
convert_tags => HASH
If present, gives a HASH reference containing tag conversion
functions. For any tags in the original to be copied whose names
appear in the hash, the name and value are passed into the
corresponding function, which should return an even-sized key/value
list giving a tag, or a list of tags, to apply to the new clone.
my @new_tags = $convert_tags->{$orig_name}->( $orig_name, $orig_value )
# Where @new_tags is ( $new_name, $new_value, $new_name_2, $new_value_2, ... )
As a further convenience, if the value for a given tag name is a
plain string instead of a code reference, it gives the new name for
the tag, and will be applied with its existing value.
If only_tags is being used too, then the source names of any tags to
be converted must also be listed there, or they will not be copied.
clone (instance)
$new = $orig->clone( %args )
Called as an instance (rather than a class) method, the newly-cloned
instance is returned in the same class as the original.
from_sprintf
$str = String::Tagged->from_sprintf( $format, @args )
Since version 0.15.
Returns a new instance of a String::Tagged object, initialised by
formatting the supplied arguments using the supplied format.
The $format string is similar to that supported by the core sprintf
operator, though a few features such as out-of-order argument indexing
and vector formatting are missing. This format string may be a plain
perl string, or an instance of String::Tagged. In the latter case, any
tags within it are preserved in the result.
In the case of a %s conversion, the value of the argument consumed may
itself be a String::Tagged instance. In this case it will be appended
to the returned object, preserving any tags within it.
All other conversions are handled individually by the core sprintf
operator and appended to the result.
join
$str = String::Tagged->join( $sep, @parts )
Since version 0.17.
Returns a new instance of a String::Tagged object, formed by
concatenating each of the component piece together, joined with the
separator string.
The result will be much like the core join function, except that it
will preserve tags in the resulting string.
METHODS
str
$str = $st->str
$str = "$st"
Returns the plain string contained within the object.
This method is also called for stringification; so the String::Tagged
object can be used in a plain string interpolation such as
my $message = String::Tagged->new( "Hello world" );
print "My message is $message\n";
length
$len = $st->length
$len = length( $st )
Returns the length of the plain string. Because stringification works
on this object class, the normal core length function works correctly
on it.
substr
$str = $st->substr( $start, $len )
Returns a String::Tagged instance representing a section from within
the given string, containing all the same tags at the same conceptual
positions.
plain_substr
$str = $st->plain_substr( $start, $len )
Returns as a plain perl string, the substring at the given position.
This will be the same string data as returned by substr, only as a
plain string without the tags
apply_tag
$st->apply_tag( $start, $len, $name, $value )
Apply the named tag value to the given extent. The tag will start on
the character at the $start index, and continue for the next $len
characters.
If $start is given as -1, the tag will be considered to start "before"
the actual string. If $len is given as -1, the tag will be considered
to end "after" end of the actual string. These special limits are used
by set_substr when deciding whether to move a tag boundary. The start
of any tag that starts "before" the string is never moved, even if more
text is inserted at the beginning. Similarly, a tag which ends "after"
the end of the string, will continue to the end even if more text is
appended.
This method returns the $st object.
$st->apply_tag( $e, $name, $value )
Alternatively, an existing String::Tagged::Extent object can be passed
as the first argument instead of two integers. The new tag will apply
at the given extent.
unapply_tag
$st->unapply_tag( $start, $len, $name )
Unapply the named tag value from the given extent. If the tag extends
beyond this extent, then any partial fragment of the tag will be left
in the string.
This method returns the $st object.
$st->unapply_tag( $e, $name )
Alternatively, an existing String::Tagged::Extent object can be passed
as the first argument instead of two integers.
delete_tag
$st->delete_tag( $start, $len, $name )
Delete the named tag within the given extent. Entire tags are removed,
even if they extend beyond this extent.
This method returns the $st object.
$st->delete_tag( $e, $name )
Alternatively, an existing String::Tagged::Extent object can be passed
as the first argument instead of two integers.
delete_all_tag
$st->delete_all_tag( $name )
Since version 0.21.
Deletes every tag with the given name. This is more efficient than
calling iter_extents to list the tags then delete_tag on each one
individually in the case of a simple name match.
This method returns the $st object.
merge_tags
$st->merge_tags( $eqsub )
Merge neighbouring or overlapping tags of the same name and equal
values.
For each pair of tags of the same name that apply on neighbouring or
overlapping extents, the $eqsub callback is called, as
$equal = $eqsub->( $name, $value_a, $value_b )
If this function returns true then the tags are merged.
The equallity test function is free to perform any comparison of the
values that may be relevant to the application; for example it may
deeply compare referred structures and check for equivalence in some
application-defined manner. In this case, the first tag of a pair is
retained, the second is deleted. This may be relevant if the tag value
is a reference to some object.
iter_extents
$st->iter_extents( $callback, %opts )
Iterate the tags stored in the string. For each tag, the CODE reference
in $callback is invoked once, being passed a String::Tagged::Extent
object that represents the extent of the tag.
$callback->( $extent, $tagname, $tagvalue )
Options passed in %opts may include:
start => INT
Start at the given position; defaults to 0.
end => INT
End after the given position; defaults to end of string. This option
overrides len.
len => INT
End after the given length beyond the start position; defaults to end
of string. This option only applies if end is not given.
only => ARRAY
Select only the tags named in the given ARRAY reference.
except => ARRAY
Select all the tags except those named in the given ARRAY reference.
Since version 0.21 it is safe to call delete_tag from within the
callback function to remove the tag currently being iterated on.
$str->iter_extents( sub {
my ( $e, $n, $v ) = @_;
$str->delete_tag( $e, $n ) if $n =~ m/^tmp_/;
} );
Apart from this scenario, the tags in the string should not otherwise
be added or removed while the iteration is occurring.
iter_tags
$st->iter_tags( $callback, %opts )
Iterate the tags stored in the string. For each tag, the CODE reference
in $callback is invoked once, being passed the start point and length
of the tag.
$callback->( $start, $length, $tagname, $tagvalue )
Options passed in %opts are the same as for iter_extents.
iter_extents_nooverlap
$st->iter_extents_nooverlap( $callback, %opts )
Iterate non-overlapping extents of tags stored in the string. The CODE
reference in $callback is invoked for each extent in the string where
no tags change. The entire set of tags active in that extent is given
to the callback. Because the extent covers possibly-multiple tags, it
will not define the anchor_before and anchor_after flags.
$callback->( $extent, %tags )
The callback will be invoked over the entire length of the string,
including any extents with no tags applied.
Options may be passed in %opts to control the range of the string
iterated over, in the same way as the iter_extents method.
If the only or except filters are applied, then only the tags that
survive filtering will be present in the %tags hash. Tags that are
excluded by the filtering will not be present, nor will their bounds be
used to split the string into extents.
iter_tags_nooverlap
$st->iter_tags_nooverlap( $callback, %opts )
Iterate extents of the string using iter_extents_nooverlap, but passing
the start and length of each extent to the callback instead of the
extent object.
$callback->( $start, $length, %tags )
Options may be passed in %opts to control the range of the string
iterated over, in the same way as the iter_extents method.
iter_substr_nooverlap
$st->iter_substr_nooverlap( $callback, %opts )
Iterate extents of the string using iter_extents_nooverlap, but passing
the substring of data instead of the extent object.
$callback->( $substr, %tags )
Options may be passed in %opts to control the range of the string
iterated over, in the same way as the iter_extents method.
tagnames
@names = $st->tagnames
Returns the set of tag names used in the string, in no particular
order.
get_tags_at
$tags = $st->get_tags_at( $pos )
Returns a HASH reference of all the tag values active at the given
position.
get_tag_at
$value = $st->get_tag_at( $pos, $name )
Returns the value of the named tag at the given position, or undef if
the tag is not applied there.
get_tag_extent
$extent = $st->get_tag_extent( $pos, $name )
If the named tag applies to the given position, returns a
String::Tagged::Extent object to represent the extent of the tag at
that position. If it does not, undef is returned. If an extent is
returned it will define the anchor_before and anchor_after flags if
appropriate.
get_tag_missing_extent
$extent = $st->get_tag_missing_extent( $pos, $name )
If the named tag does not apply at the given position, returns the
extent of the string around that position that does not have the tag.
If it does exist, undef is returned. If an extent is returned it will
not define the anchor_before and anchor_after flags, as these do not
make sense for the range in which a tag is absent.
set_substr
$st->set_substr( $start, $len, $newstr )
Modifies a extent of the underlying plain string to that given. The
extents of tags in the string are adjusted to cope with the modified
region, and the adjustment in length.
Tags entirely before the replaced extent remain unchanged.
Tags entirely within the replaced extent are deleted.
Tags entirely after the replaced extent are moved by appropriate amount
to ensure they still apply to the same characters as before.
Tags that start before and end after the extent remain, and have their
lengths suitably adjusted.
Tags that span just the start or end of the extent, but not both, are
truncated, so as to remove the part of the tag applied on the modified
extent but preserving that applied outside.
If $newstr is a String::Tagged object, then its tags will be applied to
$st as appropriate. Edge-anchored tags in $newstr will not be extended
through $st, though they will apply as edge-anchored if they now sit at
the edge of the new string.
insert
$st->insert( $start, $newstr )
Insert the given string at the given position. A shortcut around
set_substr.
If $newstr is a String::Tagged object, then its tags will be applied to
$st as appropriate. If $start is 0, any before-anchored tags in will
become before-anchored in $st.
append
$st->append( $newstr )
$st .= $newstr
Append to the underlying plain string. A shortcut around set_substr.
If $newstr is a String::Tagged object, then its tags will be applied to
$st as appropriate. Any after-anchored tags in will become
after-anchored in $st.
append_tagged
$st->append_tagged( $newstr, %tags )
Append to the underlying plain string, and apply the given tags to the
newly-inserted extent.
Returns $st itself so that the method may be easily chained.
concat
$ret = $st->concat( $other )
$ret = $st . $other
Returns a new String::Tagged containing the two strings concatenated
together, preserving any tags present. This method overloads normal
string concatenation operator, so expressions involving String::Tagged
values retain their tags.
This method or operator tries to respect subclassing; preferring to
return a new object of a subclass if either argument or operand is a
subclass of String::Tagged. If they are both subclasses, it will prefer
the type of the invocant or first operand.
matches
@subs = $st->matches( $regexp )
Returns a list of substrings (as String::Tagged instances) for every
non-overlapping match of the given $regexp.
This could be used, for example, to build a formatted string from a
formatted template containing variable expansions:
my $template = ...
my %vars = ...
my $ret = String::Tagged->new;
foreach my $m ( $template->matches( qr/\$\w+|[^$]+/ ) ) {
if( $m =~ m/^\$(\w+)$/ ) {
$ret->append_tagged( $vars{$1}, %{ $m->get_tags_at( 0 ) } );
}
else {
$ret->append( $m );
}
}
This iterates segments of the template containing variables expansions
starting with a $ symbol, and replaces them with values from the %vars
hash, careful to preserve all the formatting tags from the original
template string.
match_extents
@extents = $st->match_extents( $regexp )
Since version 0.20.
Returns a list of extent objects for every non-overlapping match of the
given $regexp. This is similar to "matches", except that the results
are returned as extent objects instead of substrings, allowing access
to the position information as well.
If using the result of this method to find regions of a string to
modify, remember that any length alterations will not update positions
in later extent objects. However, since the extents are non-overlapping
and in position order, this can be handled by iterating them in reverse
order so that the modifications done first are later in the string.
foreach my $e ( reverse $st->match_extents( $pattern ) ) {
$st->set_substr( $e->start, $e->length, $replacement );
}
split
@parts = $st->split( $regexp, $limit )
Returns a list of substrings by applying the regexp to the string
content; similar to the core perl split function. If $limit is
supplied, the method will stop at that number of elements, returning
the entire remainder of the input string as the final element. If the
$regexp contains a capture group then the content of the first one will
be added to the return list as well.
sprintf
$ret = $st->sprintf( @args )
Since version 0.15.
Returns a new string by using the given instance as the format string
for a "from_sprintf" constructor call. The returned instance will be of
the same class as the invocant.
debug_sprintf
$ret = $st->debug_sprintf
Returns a representation of the string data and all the tags, suitable
for debug printing or other similar use. This is a format such as is
given in the DESCRIPTION section above.
The output will consist of a number of lines, the first containing the
plain underlying string, then one line per tag. The line shows the
extent of the tag given by [---] markers, or a | in the special case of
a tag covering only a single character. Special markings of < and >
indicate tags which are "before" or "after" anchored.
For example:
Hello, world
[---] word => 1
<[----------]> everywhere => 1
| space => 1
TODO
* There are likely variations on the rules for set_substr that could
equally apply to some uses of tagged strings. Consider whether the
behaviour of modification is chosen per-method, per-tag, or
per-string.
* Consider how to implement a clone from one tag format to another
which wants to merge multiple different source tags together into a
single new one.
AUTHOR
Paul Evans