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    my ($elem) = @_;

    my $string = $elem->string();

    $string eq q<@{}>           ## no critic (RequireInterpolationOfMetachars)
        or $string eq q<${}>    ## no critic (RequireInterpolationOfMetachars)
        or return;

    my $statement = $elem;
    while ( not $statement->isa('PPI::Statement::Include') ) {
        $statement = $statement->parent() or return;
    }

    return if $statement->type() ne q<use>;
    return $statement->module() eq q<overload>;
}

#-----------------------------------------------------------------------------

sub _looks_like_use_vars {
    my ($elem) = @_;

    my $string = $elem->string();

    my $statement = $elem;
    while ( not $statement->isa('PPI::Statement::Include') ) {
        $statement = $statement->parent() or return;
    }

    return if $statement->type() ne q<use>;
    return $statement->module() eq q<vars>;
}

1;

__END__

#-----------------------------------------------------------------------------

=pod

=for stopwords RCS

=head1 NAME

Perl::Critic::Policy::ValuesAndExpressions::RequireInterpolationOfMetachars - Warns that you might have used single quotes when you really wanted double-quotes.


=head1 AFFILIATION

This Policy is part of the core L<Perl::Critic|Perl::Critic>
distribution.


=head1 DESCRIPTION

This policy warns you if you use single-quotes or C<q//> with a string
that has unescaped metacharacters that may need interpolation. Its
hard to know for sure if a string really should be interpolated
without looking into the symbol table.  This policy just makes an
educated guess by looking for metacharacters and sigils which usually
indicate that the string should be interpolated.


=head2 Exceptions

=over

=item *

C<${}> and C<@{}> in a C<use overload>:

    use overload '${}' => \&deref,     # ok
                 '@{}' => \&arrayize;  # ok

=item *

Variable names to C<use vars>:

    use vars '$x';          # ok
    use vars ('$y', '$z');  # ok
    use vars qw< $a $b >;   # ok


=item *

Things that look like e-mail addresses:

    print 'john@foo.com';           # ok
    $address = 'suzy.bar@baz.net';  # ok

=back


=head1 CONFIGURATION

The C<rcs_keywords> option allows you to stop this policy from complaining
about things that look like RCS variables, for example, in deriving values for
C<$VERSION> variables.

For example, if you've got code like

    our ($VERSION) = (q<$Revision: 3843 $> =~ m/(\d+)/mx);

You can specify

    [ValuesAndExpressions::RequireInterpolationOfMetachars]
    rcs_keywords = Revision

in your F<.perlcriticrc> to provide an exemption.


=head1 NOTES

Perl's own C<warnings> pragma also warns you about this.


=head1 SEE ALSO

L<Perl::Critic::Policy::ValuesAndExpressions::ProhibitInterpolationOfLiterals|Perl::Critic::Policy::ValuesAndExpressions::ProhibitInterpolationOfLiterals>