builtin(3p) Perl Programmers Reference Guide builtin(3p) #
builtin(3p) Perl Programmers Reference Guide builtin(3p)
NNAAMMEE #
builtin - Perl pragma to import built-in utility functions
SSYYNNOOPPSSIISS #
use builtin qw(
true false is_bool
weaken unweaken is_weak
blessed refaddr reftype
created_as_string created_as_number
ceil floor
trim
);
DDEESSCCRRIIPPTTIIOONN #
Perl provides several utility functions in the "builtin" package. These
are plain functions, and look and behave just like regular user-defined
functions do. They do not provide new syntax or require special parsing.
These functions are always present in the interpreter and can be called
at any time by their fully-qualified names. By default they are not
available as short names, but can be requested for convenience.
Individual named functions can be imported by listing them as import
parameters on the "use" statement for this pragma.
The overall "builtin" mechanism, as well as every individual function it
provides, are currently eexxppeerriimmeennttaall.
WWaarrnniinngg: At present, the entire "builtin" namespace is experimental.
Calling functions in it will trigger warnings of the
"experimental::builtin" category.
LLeexxiiccaall IImmppoorrtt This pragma module creates _l_e_x_i_c_a_l aliases in the currently-compiling scope to these builtin functions. This is similar to the lexical effect of other pragmas such as strict and feature.
sub classify
{
my $val = shift;
use builtin 'is_bool';
return is_bool($val) ? "boolean" : "not a boolean";
}
# the is_bool() function is no longer visible here
# but may still be called by builtin::is_bool()
Because these functions are imported lexically, rather than by package
symbols, the user does not need to take any special measures to ensure
they don't accidentally appear as object methods from a class.
package An::Object::Class {
use builtin 'true', 'false';
...
}
# does not appear as a method
An::Object::Class->true;
# Can't locate object method "true" via package "An::Object::Class"
# at ...
FFUUNNCCTTIIOONNSS #
ttrruuee $val = true;
Returns the boolean truth value. While any scalar value can be tested for
truth and most defined, non-empty and non-zero values are considered
"true" by perl, this one is special in that "is_bool" considers it to be
a distinguished boolean value.
This gives an equivalent value to expressions like "!!1" or "!0".
ffaallssee $val = false;
Returns the boolean fiction value. While any non-true scalar value is
considered "false" by perl, this one is special in that "is_bool"
considers it to be a distinguished boolean value.
This gives an equivalent value to expressions like "!!0" or "!1".
iiss__bbooooll $bool = is_bool($val);
Returns true when given a distinguished boolean value, or false if not. A
distinguished boolean value is the result of any boolean-returning
builtin function (such as "true" or "is_bool" itself), boolean-returning
operator (such as the "eq" or "==" comparison tests or the "!" negation
operator), or any variable containing one of these results.
This function used to be named "isbool". A compatibility alias is
provided currently but will be removed in a later version.
wweeaakkeenn weaken($ref);
Weakens a reference. A weakened reference does not contribute to the
reference count of its referent. If only weakened references to a
referent remain, it will be disposed of, and all remaining weak
references to it will have their value set to "undef".
uunnwweeaakkeenn unweaken($ref);
Strengthens a reference, undoing the effects of a previous call to
"weaken".
iiss__wweeaakk $bool = is_weak($ref);
Returns true when given a weakened reference, or false if not a reference
or not weak.
This function used to be named "isweak". A compatibility alias is
provided currently but will be removed in a later version.
bblleesssseedd $str = blessed($ref);
Returns the package name for an object reference, or "undef" for a non-
reference or reference that is not an object.
rreeffaaddddrr $num = refaddr($ref);
Returns the memory address for a reference, or "undef" for a non-
reference. This value is not likely to be very useful for pure Perl
code, but is handy as a means to test for referential identity or
uniqueness.
rreeffttyyppee $str = reftype($ref);
Returns the basic container type of the referent of a reference, or
"undef" for a non-reference. This is returned as a string in all-
capitals, such as "ARRAY" for array references, or "HASH" for hash
references.
ccrreeaatteedd__aass__ssttrriinngg $bool = created_as_string($val);
Returns a boolean representing if the argument value was originally
created as a string. It will return true for any scalar expression whose
most recent assignment or modification was of a string-like nature - such
as assignment from a string literal, or the result of a string operation
such as concatenation or regexp. It will return false for references
(including any object), numbers, booleans and undef.
It is unlikely that you will want to use this for regular data validation
within Perl, as it will not return true for regular numbers that are
still perfectly usable as strings, nor for any object reference -
especially objects that overload the stringification operator in an
attempt to behave more like strings. For example
my $val = URI->new( "https://metacpan.org/" );
if( created_as_string $val ) { ... } # this will not execute
ccrreeaatteedd__aass__nnuummbbeerr $bool = created_as_number($val);
Returns a boolean representing if the argument value was originally
created as a number. It will return true for any scalar expression whose
most recent assignment or modification was of a numerical nature - such
as assignment from a number literal, or the result of a numerical
operation such as addition. It will return false for references
(including any object), strings, booleans and undef.
It is unlikely that you will want to use this for regular data validation
within Perl, as it will not return true for regular strings of decimal
digits that are still perfectly usable as numbers, nor for any object
reference - especially objects that overload the numification operator in
an attempt to behave more like numbers. For example
my $val = Math::BigInt->new( 123 );
if( created_as_number $val ) { ... } # this will not execute
While most Perl code should operate on scalar values without needing to
know their creation history, these two functions are intended to be used
by data serialisation modules such as JSON encoders or similar
situations, where language interoperability concerns require making a
distinction between values that are fundamentally stringlike versus
numberlike in nature.
cceeiill $num = ceil($num);
Returns the smallest integer value greater than or equal to the given
numerical argument.
fflloooorr $num = floor($num);
Returns the largest integer value less than or equal to the given
numerical argument.
iinnddeexxeedd @ivpairs = indexed(@items)
Returns an even-sized list of number/value pairs, where each pair is
formed of a number giving an index in the original list followed by the
value at that position in it. I.e. returns a list twice the size of the
original, being equal to
(0, $items[0], 1, $items[1], 2, $items[2], ...)
Note that unlike the core "values" function, this function returns copies
of its original arguments, not aliases to them. Any modifications of
these copies are _n_o_t reflected in modifications to the original.
my @x = ...;
$_++ for indexed @x; # The @x array remains unaffected
This function is primarily intended to be useful combined with multi-
variable "foreach" loop syntax; as
foreach my ($index, $value) (indexed LIST) {
...
}
In scalar context this function returns the size of the list that it
would otherwise have returned, and provokes a warning in the "scalar"
category.
ttrriimm $stripped = trim($string);
Returns the input string with whitespace stripped from the beginning and
end. ttrriimm(()) will remove these characters:
" ", an ordinary space.
"\t", a tab.
"\n", a new line (line feed).
"\r", a carriage return.
and all other Unicode characters that are flagged as whitespace. A
complete list is in "Whitespace" in perlrecharclass.
$var = " Hello world "; # "Hello world"
$var = "\t\t\tHello world"; # "Hello world"
$var = "Hello world\n"; # "Hello world"
$var = "\x{2028}Hello world\x{3000}"; # "Hello world"
"trim" is equivalent to:
$str =~ s/\A\s+|\s+\z//urg;
For Perl versions where this feature is not available look at the
String::Util module for a comparable implementation.
SSEEEE AALLSSOO #
perlop, perlfunc, Scalar::Util
perl v5.36.3 2023-02-15 builtin(3p)