我看到了这个问题：
Is there any difference between “standard” and block package declaration?并考虑了主要的包装.当我编写脚本时,例如：
---- begin of the file --- #!/usr/bin/perl #probably removed by shell? my $var; #defined from now up to the end of file ... ---- end of the file ----
这自动进入主包,所以我理解正确的下一个发生.
---- begin of the file ---
{ #<-- 1st line
package main;
my $var; #variable transformed to block scope - "up to the end of block"
...
} # <-- last line
---- end of the file ----
这相当于
---- begin of the file ---
package main { #1st line
my $var; #variable block scope
...
} #last line
---- end of the file ----
问题1：以上是对的吗？主包发生了什么？
现在是BEGIN / END块和pragma.如果我理解的话,在编译阶段处理.所以有：
---- begin of the file ---
#!/usr/bin/perl
use strict; #file scope
use warnings; #file scope
my $var; #defined from now up to the end of file
BEGIN {
say $var; #the $var is not known here - but it is declared
}
...
---- end of the file ----
声明$var,但在这里
---- begin of the file ---
#!/usr/bin/perl
use strict; #file scope
use warnings; #file scope
BEGIN {
say $var; #the $var is not known here - but "requires explicit package name" error
}
my $var; #defined from now up to the end of file
...
---- end of the file ----
$var未声明.
那么如何将上述内容翻译成“默认主包”？
它始终是：
---- begin of the file ---
{
package main;
use strict; #block scope ???
use warnings; #block scope ???
my $var; #defined from now up to the end of block
BEGIN { #NESTED???
say $var; #the $var is not known here - but declared
}
...
}
---- end of the file ----
相当于
---- begin of the file ---
package main {
use strict; #block scope
use warnings; #block scope
my $var; #defined from now up to the end of block
BEGIN { #NESTED block
say $var;
}
...
}
---- end of the file ----
问题是 – 在这里_ANY使用类似的东西：
---- begin of the file ---
use strict; #always should be at the START OF THE FILE - NOT IN BLOCKS?
use warnings;
#not NESTED
BEGIN {
}
package main {
my $var;
}
所以问题是：
>在BLOCK语法的上下文中,如何处理pragma,BEGIN / END / CHECK块和主包？
>将“文件范围”更改为“块范围”时 – 或者如果它没有更改,“标准主程序包”到“主程序包{block}”的等效转换是什么？
和最后一个代码：
---- begin of the file ---
use strict; #always should be at the START OF THE FILE - NOT IN BLOCKS?
use warnings;
my $var;
#not NESTED
BEGIN {
}
package main {
}
我的$var如何进入主包？所以这被翻译成：
---- begin of the file ---
use strict; #always should be at the START OF THE FILE - NOT IN BLOCKS?
use warnings;
#not NESTED
BEGIN {
}
package main {
my $var; #### GETS HERE????
}
对不起文字墙…
解决方法
使用my声明变量时,它不在任何包中.完全没有.块范围与任何包都严格不同.该变量在最内层封闭块的右括号(})之前有效,但没有包限定.如果你写了$main :: var或$:: var,它将是不同的变量.
use warnings;
use strict;
package main {
my $var = 'this';
}
$var; # error,$var was not declared in this scope
say $main::var; # says nothing
还有两种方法可以声明变量：
>使用vars qw($var)使$var引用包中的当前包中的变量.
>我们的$var使得$var引用当前块中我们语句时当前包中的变量.
块包声明是一个块,并将其内容放在包中.而无块包声明将以下内容放在另一个包中,但当前块范围仍在继续.
另一个缺失的是你写的时候
use warnings;
use strict;
package main {
# ...
}
你有效地写了
package main {
use warnings;
use strict;
package main {
# ...
}
}
因为包装是相同的,所以是相同的
package main {
use warnings;
use strict;
{
# ...
}
}
换句话说,包在文件开头是主要的,并且隐式块作用域(文件范围)是打开的.当您重新进入主程序包时,它没有任何效果,如果它与程序段关联,它的行为就像任何程序段一样.