和仙子等众高手一起探讨一个问题 - Chinaunix

'符号名称' => 指向 typeglob 的引用

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'值类型' => 值引用

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${*{$::{sym}}{HASH}{name}

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*pkg::sym{HASH} # 和 \%pkg::sym 一样

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our %hash = ( a=>1 );
my $glob = *hash;

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#!/usr/bin/perl
our %hash = ( a=>1);
my $glob = *hash;
print ${$glob}{a}."\n";

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print ref $glob, "\n";
print ref \$glob, "\n";

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our $hash = 'not_a_hash';
our %hash = ( a=>1 );
my $glob = *hash;
print ${$glob};
__END__
output is 'not_a_hash'

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our %hash = ( a => 1 );
my $glob = \%hash;
print ${$glob}{a};
__END__
output is '1';

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our %hash = ( a=>1 );
my $glob = *hash;

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A Strange Syntax
7 封邮件
--------------------------------------------------------------------------------
Jennifer Garner <mlists.j@gmail.com> 2005年12月5日下午9:52
收件人: beginners@perl.org
Hi,lists,
Seeing this code please:
our %sym = (
name => 'flower',
age => 23,
);
print ${*{$::{sym}}{HASH}}{name};
The result of printing is : flower.
How to analyse the last sentence of that code?Thanks.
--------------------------------------------------------------------------------
Adriano Ferreira <a.r.ferreira@gmail.com> 2005年12月5日下午10:53
收件人: Jennifer Garner <mlists.j@gmail.com>, beginners@perl.org
On 12/5/05, Jennifer Garner <mlists.j@gmail.com> wrote:
> print ${*{$::{sym}}{HASH}}{name};
> How to analyse the last sentence of that code?Thanks.
From "perldoc perlref"
7. A reference can be created by using a special syntax, lovingly
known as the *foo{THING} syntax. *foo{THING} returns a reference
to the THING slot in *foo (which is the symbol table entry which
holds everything known as foo).
$scalarref = *foo{SCALAR};
$arrayref = *ARGV{ARRAY};
$hashref = *ENV{HASH};
$coderef = *handler{CODE};
$ioref = *STDIN{IO};
$globref = *foo{GLOB};
So $::{sym} returns the glob symbol "sym" on the main package ($main::
or $::), takes a reference to its HASH part, and returns what it got
in the key "name". Piece of cake, ain't it?
Regards,
Adriano.
--
To unsubscribe, e-mail: beginners-unsubscribe@perl.org
For additional commands, e-mail: beginners-help@perl.org
<http://learn.perl.org/> <http://learn.perl.org/first-response>
--------------------------------------------------------------------------------
Wiggins d'Anconia <wiggins@danconia.org> 2005年12月6日上午2:33
收件人: Adriano Ferreira <a.r.ferreira@gmail.com>
抄送: Jennifer Garner <mlists.j@gmail.com>, beginners@perl.org
Adriano Ferreira wrote:
> On 12/5/05, Jennifer Garner <mlists.j@gmail.com> wrote:
>
>>print ${*{$::{sym}}{HASH}}{name};
>
>
>>How to analyse the last sentence of that code?Thanks.
>
>
>>From "perldoc perlref"
>
> 7. A reference can be created by using a special syntax, lovingly
> known as the *foo{THING} syntax. *foo{THING} returns a reference
> to the THING slot in *foo (which is the symbol table entry which
> holds everything known as foo).
>
> $scalarref = *foo{SCALAR};
> $arrayref = *ARGV{ARRAY};
> $hashref = *ENV{HASH};
> $coderef = *handler{CODE};
> $ioref = *STDIN{IO};
> $globref = *foo{GLOB};
>
> So $::{sym} returns the glob symbol "sym" on the main package ($main::
> or $::), takes a reference to its HASH part, and returns what it got
> in the key "name". Piece of cake, ain't it?
>
> Regards,
> Adriano.
>
Now that you understand it, replace it with $sym->{name} so the next
person doesn't have to ask. Unless you are using a really old Perl.
http://danconia.org
[引用文字已隐藏]
--------------------------------------------------------------------------------
Flemming Greve Skovengaard <dsl58893@vip.cybercity.dk> 2005年12月6日上午3:05
收件人: "beginners@perl.org" <beginners@perl.org>
抄送: Wiggins d'Anconia <wiggins@danconia.org>
Wiggins d'Anconia wrote:
>
> Now that you understand it, replace it with $sym->{name} so the next
> person doesn't have to ask. Unless you are using a really old Perl.
>
Actually that should be *sym->{name} instead of $sym->{name} ( or %sym->{name}
but that's deprecated ).
Else you get "Variable "$sym" is not imported at ..." when using 'use strict;'
( as you should ).
--
Flemming Greve Skovengaard The prophecy of the holy Norns
a.k.a Greven, TuxPower The world is doomed to die
<dsl58893@vip.cybercity.dk> Fire in the sky
4112.38 BogoMIPS The end is coming soon
[引用文字已隐藏]
--------------------------------------------------------------------------------
Jennifer Garner <mlists.j@gmail.com> 2005年12月6日上午9:10
收件人: Flemming Greve Skovengaard <dsl58893@vip.cybercity.dk>
抄送: "beginners@perl.org" <beginners@perl.org>, Wiggins d'Anconia <wiggins@danconia.org>
${*{$::{sym}}{HASH}}{name};
As we know, $::{sym} == *main::sym, it's a typeglob.
but what is **main::sym? and the same,what is *{$glob}?thanks.
[引用文字已隐藏]
--------------------------------------------------------------------------------
Adriano Ferreira <a.r.ferreira@gmail.com> 2005年12月7日上午12:26
收件人: Jennifer Garner <mlists.j@gmail.com>, beginners@perl.org
On 12/5/05, Jennifer Garner <mlists.j@gmail.com> wrote:
> As we know, $::{sym} == *main::sym, it's a typeglob.
> but what is **main::sym? and the same,what is *{$glob}?thanks.
**main::sym is a syntax error, but *{*main::sym}==*main::sym.
But don't be fooled by the equality $::{sym} == *main::sym. It just
means they numerically compare the same. Taking references you get
that $::{sym} returns a scalar and *main::sym a glob.
$ perl -e 'print \($::sym, *main::sym)'
SCALAR(0x1002f094)GLOB(0x10010fa8)
So *{$glob} is the way to tell Perl to go from the scalar to the glob,
when we'll be able to access its HASH part.
That's why
$ perl -e 'our %sym = (name => "flower"); print ${*{$::{sym}}{HASH}}{name};"
prints "flower", but
$ perl -e 'our %sym = (name => "flower"); print ${$::{sym}{HASH}}{name};"
prints nothing ($::{sym}{HASH} returns undef). As Wiggins wisely said,
$sym->{name} is more sane.
--
[引用文字已隐藏]
--------------------------------------------------------------------------------
Jennifer Garner <mlists.j@gmail.com> 2005年12月7日上午9:16
收件人: "beginners@perl.org" <beginners@perl.org>
Thanks for Adriano Ferreira.Your explaination is good for me.I have known
that.
[引用文字已隐藏]

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typedef enum {
SVt_NULL, /* 0 */
SVt_IV, /* 1 */
SVt_NV, /* 2 */
SVt_RV, /* 3 */
SVt_PV, /* 4 */
SVt_PVIV, /* 5 */
SVt_PVNV, /* 6 */
SVt_PVMG, /* 7 */
SVt_PVBM, /* 8 */
SVt_PVLV, /* 9 */
SVt_PVAV, /* 10 */
SVt_PVHV, /* 11 */
SVt_PVCV, /* 12 */
SVt_PVGV, /* 13 */
SVt_PVFM, /* 14 */
SVt_PVIO /* 15 */
} svtype;

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