—use
5.010001;
use
strict;
use
warnings;
use
Readonly;
our
$VERSION
=
'1.152'
;
#-----------------------------------------------------------------------------
Readonly::Scalar
my
$DESC
=>
q{Negative array index should be used}
;
Readonly::Scalar
my
$EXPL
=> [ 88 ];
#-----------------------------------------------------------------------------
sub
supported_parameters {
return
() }
sub
default_severity {
return
$SEVERITY_HIGH
}
sub
default_themes {
return
qw( core maintenance pbp )
}
sub
applies_to {
return
'PPI::Structure::Subscript'
}
#-----------------------------------------------------------------------------
sub
violates {
my
(
$self
,
$elem
,
$doc
) =
@_
;
return
if
$elem
->braces ne
'[]'
;
my
(
$name
,
$isref
) = _is_bad_index(
$elem
);
return
if
( !
$name
);
return
if
!_is_array_name(
$elem
,
$name
,
$isref
);
return
$self
->violation(
$DESC
,
$EXPL
,
$elem
);
}
Readonly::Scalar
my
$MAX_EXPRESSION_COMPLEXITY
=> 4;
sub
_is_bad_index {
# return (varname, 0|1) if this could be a violation
my
(
$elem
) =
@_
;
my
@children
=
$elem
->schildren();
return
if
@children
!= 1;
# too complex
return
if
!
$children
[0]->isa(
'PPI::Statement::Expression'
);
# too complex
# This is the expression elements that compose the array indexing
my
@expr
=
$children
[0]->schildren();
return
if
!
@expr
||
@expr
>
$MAX_EXPRESSION_COMPLEXITY
;
my
(
$name
,
$isref
,
$isindex
) = _is_bad_var_in_index(\
@expr
);
return
if
!
$name
;
return
$name
,
$isref
if
!
@expr
&&
$isindex
;
return
if
!_is_minus_number(
@expr
);
return
$name
,
$isref
;
}
sub
_is_bad_var_in_index {
# return (varname, isref=0|1, isindex=0|1) if this could be a violation
my
(
$expr
) =
@_
;
if
(
$expr
->[0]->isa(
'PPI::Token::ArrayIndex'
) ) {
# [$#arr]
return
_arrayindex(
$expr
);
}
elsif
(
$expr
->[0]->isa(
'PPI::Token::Cast'
) ) {
# [$#{$arr} ...] or [$#$arr ...] or [@{$arr} ...] or [@$arr ...]
return
_cast(
$expr
);
}
elsif
(
$expr
->[0]->isa(
'PPI::Token::Symbol'
)) {
# [@arr ...]
return
_symbol(
$expr
);
}
return
;
}
sub
_arrayindex {
# return (varname, isref=0|1, isindex=0|1) if this could be a violation
my
(
$expr
) =
@_
;
my
$arrindex
=
shift
@{
$expr
};
if
(
$arrindex
->content =~ m/\A \$[
#] (.*) \z /xms) { # What else could it be???
return
$1, 0, 1;
}
return
;
}
sub
_cast {
# return (varname, isref=0|1, isindex=0|1) if this could be a violation
my
(
$expr
) =
@_
;
my
$cast
=
shift
@{
$expr
};
if
(
$cast
eq
q{$#}
||
$cast
eq
q{@}
) { ##
no
critic(RequireInterpolationOfMetachars)
my
$isindex
=
$cast
eq
q{$#}
? 1 : 0; ##
no
critic(RequireInterpolationOfMetachars)
my
$arrvar
=
shift
@{
$expr
};
if
(
$arrvar
->isa(
'PPI::Structure::Block'
)) {
# look for [$#{$arr} ...] or [@{$arr} ...]
my
@blockchildren
=
$arrvar
->schildren();
return
if
@blockchildren
!= 1;
return
if
!
$blockchildren
[0]->isa(
'PPI::Statement'
);
my
@ggg
=
$blockchildren
[0]->schildren;
return
if
@ggg
!= 1;
return
if
!
$ggg
[0]->isa(
'PPI::Token::Symbol'
);
if
(
$ggg
[0] =~ m/\A \$ (.*) \z/xms) {
return
$1, 1,
$isindex
;
}
}
elsif
(
$arrvar
->isa(
'PPI::Token::Symbol'
) ) {
# look for [$#$arr ...] or [@$arr ...]
if
(
$arrvar
=~ m/\A \$ (.*) \z/xms) {
return
$1, 1,
$isindex
;
}
}
}
return
;
}
sub
_symbol {
# return (varname, isref=0|1, isindex=0|1) if this could be a violation
my
(
$expr
) =
@_
;
my
$arrvar
=
shift
@{
$expr
};
if
(
$arrvar
=~ m/\A \@ (.*) \z/xms) {
return
$1, 0, 0;
}
return
;
}
sub
_is_minus_number {
# return true if @expr looks like "- n"
my
@expr
=
@_
;
return
if
!
@expr
;
return
if
@expr
!= 2;
my
$op
=
shift
@expr
;
return
if
!
$op
->isa(
'PPI::Token::Operator'
);
return
if
$op
ne
q{-}
;
my
$number
=
shift
@expr
;
return
if
!
$number
->isa(
'PPI::Token::Number'
);
return
1;
}
sub
_is_array_name {
# return true if name and isref matches
my
(
$elem
,
$name
,
$isref
) =
@_
;
my
$sib
=
$elem
->sprevious_sibling;
return
if
!
$sib
;
if
(
$sib
->isa(
'PPI::Token::Operator'
) &&
$sib
eq
'->'
) {
return
if
( !
$isref
);
$isref
= 0;
$sib
=
$sib
->sprevious_sibling;
return
if
!
$sib
;
}
return
if
!
$sib
->isa(
'PPI::Token::Symbol'
);
return
if
$sib
!~ m/\A \$ \Q
$name
\E \z/xms;
my
$cousin
=
$sib
->sprevious_sibling;
return
if
$isref
^ _is_dereferencer(
$cousin
);
return
if
$isref
&& _is_dereferencer(
$cousin
->sprevious_sibling );
return
$elem
;
}
sub
_is_dereferencer {
# must return 0 or 1, not undef
my
$elem
=
shift
;
return
0
if
!
$elem
;
return
1
if
$elem
->isa(
'PPI::Token::Operator'
) &&
$elem
eq
'->'
;
return
1
if
$elem
->isa(
'PPI::Token::Cast'
);
return
0;
}
1;
#-----------------------------------------------------------------------------
__END__
=pod
=for stopwords performant
=head1 NAME
Perl::Critic::Policy::Variables::RequireNegativeIndices - Negative array index should be used.
=head1 AFFILIATION
This Policy is part of the core L<Perl::Critic|Perl::Critic>
distribution.
=head1 DESCRIPTION
Perl treats a negative array subscript as an offset from the end. Given
this, the preferred way to get the last element is C<$x[-1]>, not
C<$x[$#x]> or C<$x[@x-1]>, and the preferred way to get the next-to-last
is C<$x[-2]>, not C<$x[$#x-1> or C<$x[@x-2]>.
The biggest argument against the non-preferred forms is that B<their
semantics change> when the computed index becomes negative. If C<@x>
contains at least two elements, C<$x[$#x-1]> and C<$x[@x-2]> are
equivalent to C<$x[-2]>. But if it contains a single element,
C<$x[$#x-1]> and C<$x[@x-2]> are both equivalent to C<$x[-1]>. Simply
put, the preferred form is more likely to do what you actually want.
As Conway points out, the preferred forms also perform better, are more
readable, and are easier to maintain.
This policy notices all of the simple forms of the above problem, but
does not recognize any of these more complex examples:
$some->[$data_structure]->[$#{$some->[$data_structure]} -1];
my $ref = \@arr; $ref->[$#arr];
=head1 CONFIGURATION
This Policy is not configurable except for the standard options.
=head1 AUTHOR
Chris Dolan <cdolan@cpan.org>
=head1 COPYRIGHT
Copyright (c) 2006-2011 Chris Dolan.
This program is free software; you can redistribute it and/or modify
it under the same terms as Perl itself.
=cut
# Local Variables:
# mode: cperl
# cperl-indent-level: 4
# fill-column: 78
# indent-tabs-mode: nil
# c-indentation-style: bsd
# End:
# ex: set ts=8 sts=4 sw=4 tw=78 ft=perl expandtab shiftround :