Perl::Critic::Policy::BuiltinFunctions::ProhibitUselessTopic(3)
NAME
Perl::Critic::Policy::BuiltinFunctions::ProhibitUselessTopic - Don't
pass $_ to built-in functions that assume it, or to most filetest
operators.
AFFILIATION
This Policy is part of the Perl::Critic distribution.
DESCRIPTION
There are a number of places where $_, or "the topic" variable, is
unnecessary.
Topic unnecessary for certain Perl built-in functions
Many Perl built-in functions will operate on $_ if no argument is
passed. For example, the "length" function will operate on $_ by
default. This snippet:
for ( @list ) {
if ( length( $_ ) == 4 ) { ...
is more idiomatically written as:
for ( @list ) {
if ( length == 4 ) { ...
In the case of the "split" function, the second argument is the one
that defaults to $_. This snippet:
for ( @list ) {
my @args = split /\t/, $_;
is better written as:
for ( @list ) {
my @args = split /\t/;
There is one built-in that this policy does not check for: "reverse"
called with $_.
The "reverse" function only operates on $_ if called in scalar context.
Therefore:
for ( @list ) {
my $backwards = reverse $_;
is better written as:
for ( @list ) {
my $backwards = reverse;
However, the distinction for scalar vs. list context on "reverse" is
not yet working. See KNOWN BUGS below.
Topic unnecessary for most filetest operators
Another place that $_ is unnecessary is with a filetest operator.
# These are identical.
my $size = -s $_;
my $size = -s;
# These are identical.
if ( -r $_ ) { ...
if ( -r ) { ...
The exception is after the "-t" filetest operator, which instead of
defaulting to $_ defaults to "STDIN".
# These are NOT identical.
if ( -t $_ ) { ...
if ( -t ) { ... # Checks STDIN, not $_
KNOWN BUGS
This policy flags a false positive on "reverse" called in list context,
since "reverse" in list context does not assume $_.
my $s = reverse( $_ ); # $_ is useless.
my @a = reverse( $_ ); # $_ is not useless here.
CONFIGURATION
This Policy is not configurable except for the standard options.
AUTHOR
Andy Lester <andy@petdance.com>
COPYRIGHT
Copyright (c) 2013 Andy Lester <andy@petdance.com>
This library is free software; you can redistribute it and/or modify it
under the terms of the Artistic License 2.0.
perl v5.28.2 Perl::Critic::Policy::BuiltinFunctions::ProhibitUselessTopic(3)
perl-critic 1.134.0 - Generated Mon Jun 3 07:19:37 CDT 2019