NAME
Scalar::IfDefined - Apply block to scalar depending on if it's defined.
SYNOPSIS
use Scalar::IfDefined qw/ifdef/;
my $hash = {
a => 1,
b => 2,
c => 3,
d => {
E => 1,
F => 2,
},
};
ifdef { $_ + 1 } $hash->{a}; # ---> 2
ifdef { $_ + 1 } $hash->{missing}; # ---> undef
ifdef { $_ + 1 } ifdef { $_->{F} } $hash->{d}; # ---> 3
ifdef { $_ + 1 } ifdef { $_->{MISSING} } $hash->{d}; # ---> undef
# Or perhaps with Perl6::Flows
use Perl6::Flows;
my $result = (
$hash->{a}
==> ifdef { $_->{F} }
==> ifdef { $_ + 1 }
); # ---> 3
EXPORT
ifdef
$ifdef
SUBROUTINES/METHODS
ifdef
Takes a block and a scalar value.
If the scalar value is undef, the block is ignored and undef is
returned straight away.
If the scalar value is defined, then the block is evaluated with $_ as
the value passed in, and the result of the block is returned.
lifdef
Like ifdef, except returns the empty list. In scalar context,
therefore, this works identically to ifdef, but when in a list (e.g. an
argument list or hashref constructor), it will return zero values if
the argument was undef.
# Creates { key => $some_value }, or { undef } and warnings:
# Odd number of elements in anonymous hash
# Use of uninitialized value in anonymous hash
my $href = {
ifdef { key => $_ } $some_value
};
# Creates { key => value }, or {}
my $href = {
lifdef { key => $_ } $some_value
};
$ifdef
Used to dereference a possibly-undef scalar.
If the scalar is undef, returns undef.
If the scalar is an object, the first argument is the method to call,
and the rest of the arguments are the method arguments.
If the scalar is an array ref, the first argument is used to index into
the array.
If the scalar is a hash ref, the first argument is used to access the
hash.
If the scalar is a code ref, the code ref is run with all the
arguments.
As a special case, if the first argument is a code ref, it will be run
with the scalar as the first argument and the other arguments as the
rest. This form allows you to use $ifdef on a simple scalar - but you
might be better off with ifdef itself for that.
The following uses will all return undef if the $scalar is undef, or
The Right Thing if not.
# Run "method_name" on $obj, if $obj is defined.
$obj->$ifdef("method_name", "argument", "argument");
# Run $coderef with two arguments if $coderef is defined.
$coderef->$ifdef("argument", "argument");
# Lowercase the zeroth element of the arrayref, or undef if either of those
# things is undef.
$arrayref->$ifdef(0)->$ifdef(sub { lc });
# Call "method_name" on $hashref->{object}, or return undef if either of
# those is undef
$hashref->$ifdef('object')->$ifdef('method_name');
AUTHOR
Nick Booker, <NMBooker at gmail.com>
BUGS
https://github.com/nmbooker/p5-Scalar-IfDefined/issues
ACKNOWLEDGEMENTS
Alastair McGowan-Douglas (ALTREUS)
For developing the $ifdef (coderef) form.
LICENSE AND COPYRIGHT
Copyright (C) 2015 Nick Booker
This program is free software; you can redistribute it and/or modify it
under the terms of either: the GNU General Public License as published
by the Free Software Foundation; or the Artistic License.
See
http://dev.perl.org/licenses/ for more information.
