perl的local问题。

QUOTE:

原帖由 shake863 于 2008-5-5 17:27 发表
##############################
my $hello = "How are you doing?";
sub test{
    local $hello = "insub";
    print $hello;
}
test();
这个出错可以理解，因为对已经用my声明的变量 不能再用local声 ...

QUOTE:

原帖由 shake863 于 2008-5-5 17:27 发表
##############################
my $hello = "How are you doing?";
sub test{
    local $hello = "insub";
    print $hello;
}
test();
这个出错可以理解，因为对已经用my声明的变量 不能再用local声 ...

CODE:

$a = "att";
my $a = "btt";

CODE:

my $a ="att";

CODE:

my $compile_time;
$compile_time;
print join " ", keys (%::);

$compile_time; #actually create two variables
my $compile_time;
print join " ", keys (%::);

QUOTE:

What these examples demonstrate is that my variables do not "live" in the package symbol tables. In the example with my $compile_time first, there is only one variable named $compile_time in the file, and it never gets into the package symbol table. In the other example, there are two separate variables named $compile_time : the global one in the symbol table, and my $compile_time , which is not in a symbol table.

QUOTE:

my ($nose, @eyes, %teeth);
our ($House, @Autos, %Kids);
local (*Spouse, $phone{HOME});
Each of these modifiers offers a different sort of "confinement" to the variables they modify. To oversimplify slightly: our confines names to a scope, local confines values to a scope, and my confines both names and values to a scope.
Each of these constructs may be assigned to, though they differ in what they actually do with the values, since they have different mechanisms for storing values. They also differ somewhat if you don't (as we didn't above) assign any values to them: my and local cause the variables in question to start out with values of undef or (), as appropriate; our, on the other hand, leaves the current value of its associated global unchanged.

Repeated our declarations do not meaningfully nest. Every nested my produces a new variable, and every nested local a new value. But every time you use our, you're talking about the same global variable, irrespective of nesting. When you assign to an our variable, the effects of that assignment persist after the scope of the declaration. That's because our never creates values; it just exposes a limited form of access to the global, which lives forever:
our $PROGRAM_NAME = "waiter";
{
    our $PROGRAM_NAME = "server";
    # Code called here sees "server".
    ...
}
# Code executed here still sees "server".

QUOTE:

原帖由 shake863 于 2008-5-5 18:34 发表
先不考虑“use strict;”的问题，

上面两段代码的区别只是 my $hello = "How are you doing?";
声明的位置不同。

我想知道的是，为什么下一段能出结果。

CODE:

#!/usr/bin/perl
my $hello = "initialized outside sub";
sub test1{
        local $::hello = "initialized inside sub";
        print "Global variable $::hello \n";
        print "Lexical variable $hello \n"
        }
test1 ();

QUOTE:

<lig@romeo:~/chinaunix>$ ./value
Global variable initialized inside sub
Lexical variable initialized outside sub

CODE:

local $::hello = "insub";