Cha*_*hak 4 perl if-statement switch-statement
在我们公司,我们使用这个代码(在最后给出)大约10年,它工作正常.
几天前我们遇到了一些问题,我们不得不重新编写完整的包,我们决定用Damian的Switch模块替换这个代码(为了提高代码的可读性).
一切都对我们很好.
后来我在Perlmonks上发现Damian把这个模块放在了下面
您不应该在生产中使用Damian模块,因为它们的目的是探索和构建未来的核心语言功能.
但它对我们来说工作正常,因为我们没有达到这个模块的限制(我猜).
现在我请大家看一下这两个实现(嵌套if else vs switch),让我知道在新的实现中使用Switch是否正常或是否为我们创造了一些未来的问题？在下面给出的代码中使用Switch是否正常或是否有任何隐藏的错误/问题？
我已经在CPAN和Perlmonks上阅读了这个模块的错误和评论,我想我们的代码远远没有碰到那些错误(我想是这样).
我们正在使用Perl 5.8.5.
PS:我知道Switch的替代品,我们given/when在Perl 5.10中,我们可以使用这里dispatch table指定的其他解决方案,但是现在我们只想比较使用Switch的新实现.
使用嵌套if else
if ($command =~ /^enter$/) {
$self->show_main_frames();
}
elsif ($command =~ /^XYZ_MENU/i) {
$self->show_main_menu($manual, $dbot);
}
elsif ($command =~ /^DBOT/i) {
$dbot->process();
}
# XML is used for the reminders-history: Request 2666
elsif ($command =~ /^XML_DBOT/i) {
$dbot->process();
}
elsif ($command =~ /^UGS/i) {
$ugsui->process();
}
elsif ($command eq "kill") {
my $login = $self->{COMMON_HASH}{login} || "";
my $su_login = $self->{CONF}->get("start", "SU_LOGIN");
if ($login eq $su_login) {
# usually only certain user with certain permission will be
# able to do this.
$self->do_error("Daemon was killed by ".$login);
$self->db_connection->disconnect();
$self->{LOG}->write("User $login killed the daemon", 0);
exit; # this 'exit' actually kill the daemon
}
else {
$self->do_error("User $login tried to kill the daemon. ".
"This incident will be reported");
$self->{LOG}->write("User $login tried to kill the daemon", 2);
}
}
elsif ($command eq "logout") {
# check if we should delete the password cookie
my $forget_me = $self->{CGI}->param("forget_me") || 0;
if ($forget_me) {
$self->{DB_PASSWORD_COOKIE}->delete_cookie();
}
$ugsui->do_logout();
# Cliff edit remove id from logged_in
$session->remove_session($session->login());
# delete the session of the user
delete $self->{SESSIONS}{$session->id()};
if ($self->{CACHE_TO_FILE}) {
my $session_data_path =
XYZ_DIR
."/code/cache/session_data"
.$session->id();
unlink($session_data_path);
}
}
# if we just login we should create all the main frames
elsif ($command eq "login") {
# if extra_param holds "command*XXX" the XXX will be placed instead of
# the command. extra_param holds pairs that are astrics-separated
my $extra_param = $cgi->param("extra_param");
$extra_param = "" if (!defined($extra_param));
$extra_param =~ /command\*([^\*]+)/i;
my $other_command = defined($1) ? $1 : "";
if ($other_command =~ /^dbot/i) { # meanwhile - works only on dbot
# commands
$command = $other_command;
# now we will get the other parameters from the extra_param
# (actually including the command that is still in the
# $extra_param)
while ($extra_param =~ /^\*?([^\*]+)\*([^\*]+)(.*)/) {
$extra_param = $3;
my $name = $1;
my $value = $2;
$cgi->param(-name => $name,
-value => $value);
}#end while
}#end if
else{
$self->show_main_frames();
}
}#end elsif
else {
$self->show_main_frames();
}#end outer else
使用Switch
switch ($command)
{
case /^enter$/ { $self->show_main_frames() }
case /^XYZ_MENU/i { $self->show_main_menu($manual, $dbot) }
case /^DBOT/i { $dbot->process() }
case /^XML_DBOT/i { $dbot->process() }
case /^UGS/i { $ugsui->process() }
case "kill" {
my $login = $self->{COMMON_HASH}{login} || "";
my $su_login = $self->{CONF}->get("start", "SU_LOGIN");
if ($login eq $su_login) {
# usually only certain user with certain permission will be
# able to do this.
$self->do_error("Daemon was killed by ".$login);
$self->db_connection->disconnect();
$self->{LOG}->write("User $login killed the daemon", 0);
exit; # this 'exit' actually kill the daemon
}
else {
$self->do_error("User $login tried to kill the daemon. ".
"This incident will be reported");
$self->{LOG}->write("User $login tried to kill the daemon", 2);
}
}
case "logout" {
# check if we should delete the password cookie
my $forget_me = $self->{CGI}->param("forget_me") || 0;
if ($forget_me) {
$self->{DB_PASSWORD_COOKIE}->delete_cookie();
}
$ugsui->do_logout();
# Cliff edit remove id from logged_in
$session->remove_session($session->login());
# delete the session of the user
delete $self->{SESSIONS}{$session->id()};
if ($self->{CACHE_TO_FILE}) {
my $session_data_path =
XYZ_DIR
."/code/cache/session_data"
.$session->id();
unlink($session_data_path);
}
}
case "login" {
# if extra_param holds "command*XXX" the XXX will be placed instead of
# the command. extra_param holds pairs that are astrics-separated
my $extra_param = $cgi->param("extra_param");
$extra_param = "" if (!defined($extra_param));
$extra_param =~ /command\*([^\*]+)/i;
my $other_command = defined($1) ? $1 : "";
if ($other_command =~ /^dbot/i)
{ # meanwhile - works only on dbot
# commands
$command = $other_command;
# now we will get the other parameters from the extra_param
# (actually including the command that is still in the
# $extra_param)
while ($extra_param =~ /^\*?([^\*]+)\*([^\*]+)(.*)/) {
$extra_param = $3;
my $name = $1;
my $value = $2;
$cgi->param(-name => $name,
-value => $value);
}#end while
}#end if
else {$self->show_main_frames();}
}
else {$self->show_main_frames();}
} # end switch
Switch自己解析源代码.这可能导致难以诊断直接使用它的代码中的错误.Switch创建的问题不是间歇性的,所以如果您的代码有效,您无需担心.
但实际上,它并没有增加太多.
使用Switch:
switch ($command) {
case /^enter$/ { $self->show_main_frames() }
case /^XYZ_MENU/i { $self->show_main_menu($manual, $dbot) }
case /^DBOT/i { $dbot->process() }
case /^XML_DBOT/i { $dbot->process() }
case /^UGS/i { $ugsui->process() }
case "kill" {
my $login = $self->{COMMON_HASH}{login} || "";
没有开关:
for ($command) {
if (/^enter$/) { $self->show_main_frames() }
elsif (/^XYZ_MENU/i) { $self->show_main_menu($manual, $dbot) }
elsif (/^DBOT/i) { $dbot->process() }
elsif (/^XML_DBOT/i) { $dbot->process() }
elsif (/^UGS/i) { $ugsui->process() }
elsif ($_ eq "kill") {
my $login = $self->{COMMON_HASH}{login} || "";
(elsif (/^kill\z/)也会工作.)
实际上Switch模块没有为您提供任何"杀手级功能"; 使用elsif语句也可以做到这一点,它是安全,稳定的,没有Switch的缺点.这是我在我的项目中得到的Switch的问题(我不再使用它了):
开关是由Perl过滤器制成的.该技术具有以下限制:
不是过滤器限制,而是模块本身的限制:
我建议使用自Perl 5.10以来可用的elsif或given..when语句.所以如果你使用perl 5.8.x - 请使用elsif.
您还可以阅读Switch文档的"限制"段落.