学习高阶Perl:迭代器问题
发布时间:2020-12-15 22:04:57 所属栏目:大数据 来源:网络整理
导读:我研究了高阶Perl书,并在第4.3.4章中讨论了迭代器问题. 代码: main_script.pl #!/perluse strict;use warnings;use FindBin qw($Bin);use lib $Bin;use Iterator_Utils qw(:all);use FlatDB;my $db = FlatDB-new("$Bin/db.csv") or die "$!";my $q = $db-qu
我研究了高阶Perl书,并在第4.3.4章中讨论了迭代器问题.
代码: main_script.pl #!/perl use strict; use warnings; use FindBin qw($Bin); use lib $Bin; use Iterator_Utils qw(:all); use FlatDB; my $db = FlatDB->new("$Bin/db.csv") or die "$!"; my $q = $db->query('STATE','NY'); while (my $rec = NEXTVAL($q) ) { print $rec; } Iterator_Utils.pm #!/perl use strict; use warnings; package Iterator_Utils; use Exporter 'import';; our @EXPORT_OK = qw(NEXTVAL Iterator append imap igrep iterate_function filehandle_iterator list_iterator); our %EXPORT_TAGS = ('all' => @EXPORT_OK); sub NEXTVAL { $_[0]->() } sub Iterator (&) { return $_[0] } FlatDB.pm #!/perl use strict; use warnings; package FlatDB; my $FIELDSEP = qr/:/; sub new { my $class = shift; my $file = shift; open my $fh,"<",$file or return; chomp(my $schema = <$fh>); my @field = split $FIELDSEP,$schema; my %fieldnum = map { uc $field[$_] => $_ } (0..$#field); bless { FH => $fh,FIELDS => @field,FIELDNUM => %fieldnum,FIELDSEP => $FIELDSEP } => $class; } use Fcntl ':seek'; sub query { my $self = shift; my ($field,$value) = @_; my $fieldnum = $self->{FIELDNUM}{uc $field}; return unless defined $fieldnum; my $fh = $self->{FH}; seek $fh,SEEK_SET; <$fh>; # discard schema line return Iterator { local $_; while (<$fh>) { chomp; my @fields = split $self->{FIELDSEP},$_,-1; my $fieldval = $fields[$fieldnum]; return $_ if $fieldval eq $value; } return; }; } db.csv LASTNAME:FIRSTNAME:CITY:STATE:OWES Adler:David:New York:NY:157.00 Ashton:Elaine:Boston:MA:0.00 Dominus:Mark:Philadelphia:PA:0.00 Orwant:Jon:Cambridge:MA:26.30 Schwern:Michael:New York:NY:149658.23 Wall:Larry:Mountain View:CA:-372.14 就像到目前为止的书一样,对吗?但是我没有得到输出(应该出现Adler和Schwern的字符串).错误消息是: Can't use string ("Adler:David:New York:NY:157.00") as a subroutine ref while "strict refs" in use at N:/Perle/Learn/Iterators/Iterator_Utils.pm line 12,<$fh> line 3. 我究竟做错了什么? 提前致谢! 解决方法
FlatDB调用Iterator,它在Iterator_Utils中定义,因此它需要从Iterator_Utils导入该函数.如果你添加
use Iterator_Utils qw(Iterator); 在包FlatDB之后,该程序将起作用. 非常感谢您发现此错误.我将此添加到the errata on the web site.如果您希望通过名称记入帐户,请将您的姓名发送给我. (编辑:李大同) 【声明】本站内容均来自网络,其相关言论仅代表作者个人观点,不代表本站立场。若无意侵犯到您的权利,请及时与联系站长删除相关内容! |