October 2022
Beginner to intermediate
390 pages
7h 5m
Chinese
Content preview from Perl语言入门（第8版）
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其他控制结构
｜
191
if ( ! ($fred =~ /\A[A-Z_]\w*\z/i) ) {
print "The value of \$fred doesn't look like a Perl identifier name.\n";
}
一般来说，我们应该选择最容易理解的方法写代码。对程序维护员来说，读得越顺，
理解起来也就越容易。如果用
if
表达比较拗口，加上否定才通顺的话，那就应该改
用
unless
。以后你就会发现，有时候只有使用
unless
才更自然。
伴随
unless
的
else
子句
其实
unless
结构也可以使用
else
子句。不过这种语法写出来比较容易叫人皱眉：
unless ($mon =~ /\AFeb/) {
print "This month has at least thirty days.\n";
} else {
print "Do you see what's going on here?\n";
}
确实有人希望能这么写，特别当第一个子句相当短（也许只有一行）而第二个子句又
有很多行的时候。不过我们可以把它改写成取反操作的
if
语句，或者干脆对调两个
代码块成为一个普通
if
控制结构：
if ($mon =~ /\AFeb/) {
print "Do you see what's going on here?\n";
} else {
print "This month has at least thirty days.\n";
}
有一点很重要，请记住，代码的读者永远可以分为两类：执行代码的机器以及维护代 ...
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.