问题描述
我写Perl已有相当一段时间了，并且总是发现新事物，而我碰到了一些有趣的事情，因为我没有对此的解释，也没有在网上找到它.
I'm writing Perl for quite some time now and always discovering new things, and I just ran into something interesting that I don't have the explanation to it, nor found it over the web.
sub a {
sub b {
print "In B\n";
}
}
b();
我怎么能从它的作用域之外调用b()呢?
how come I can call b() from outside its scope and it works?
我知道这样做是一种不好的做法，但我不这样做，我在这些情况下使用了闭包之类的方法，但是只是看到了.
I know its a bad practice to do it, and I dont do it, I use closured and such for these cases, but just saw that.
推荐答案
子例程在编译时存储在全局名称空间中.在您的示例中，b();是main::b();的简写.为了将功能的可见性限制在范围内，您需要为变量分配匿名子例程.
Subroutines are stored in a global namespace at compile time. In your example b(); is short hand for main::b();. To limit visibility of a function to a scope you need to assign an anonymous subroutines to a variable.
命名子例程和匿名子例程都可以形成闭包，但是由于命名子例程仅在嵌套时才编译一次，所以它们的行为并不像人们期望的那样.
Both named and anonymous subroutines can form closures, but since named subroutines are only compiled once if you nest them they don't behave as many people expect.
use warnings;
sub one {
my $var = shift;
sub two {
print "var: $var\n";
}
}
one("test");
two();
one("fail");
two();
__END__
output:
Variable "$var" will not stay shared at -e line 5.
var: test
var: test
Perl中允许嵌套命名子例程，但是几乎可以肯定，这表明该代码未正确执行某些操作.
Nesting named subroutines is allowed in Perl but it's almost certainly a sign that the code is doing someting incorrectly.
这篇关于Perl中的嵌套子例程和作用域的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！