Perl::Critic::Policy::BuiltinFunctions::ProhibitUselessTopic - Don't pass $_ to built-in functions that assume it, or to most filetest operators.
This Policy is part of the Perl::Critic distribution.
There are a number of places where $_, or "the topic" variable, is unnecessary.
$_
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:
length
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:
split
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 $_.
reverse
The reverse function only operates on $_ if called in scalar context. Therefore:
for ( @list ) { my $backwards = reverse $_;
for ( @list ) { my $backwards = reverse;
However, the distinction for scalar vs. list context on reverse is not yet working. See KNOWN BUGS below.
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.
-t
STDIN
# These are NOT identical. if ( -t $_ ) { ... if ( -t ) { ... # Checks STDIN, not $_
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.
This Policy is not configurable except for the standard options.
Andy Lester <andy@petdance.com>
Copyright (c) 2013 Andy Lester <andy@petdance.com>
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To install Perl::Critic, copy and paste the appropriate command in to your terminal.
cpanm
cpanm Perl::Critic
CPAN shell
perl -MCPAN -e shell install Perl::Critic
For more information on module installation, please visit the detailed CPAN module installation guide.