scope - 在子中通过名称获取符号的值

Question

我正在制作一个包，我必须在子程序中通过其名称获取符号的值，而符号是在子程序之外定义的。

这是简化的代码，它按预期工作:

#! /usr/bin/env perl6 

sub dump_value($symbol) {
    say ::("$symbol")
}

# usage:
my $x = 10;
dump_value('$x');

# expected output: 10
# actual output: 10

然后我将“dump_value”放在一个独立文件中，如下所示:

# somelib.pm6
unit module somelib;

sub dump_value($symbol) is export {
    say ::("$symbol")
}

# client.pl6
#! /usr/bin/env perl6

use lib ".";
use somelib;

my $x = 10;

dump_value('$x');

编译器提示:

No such symbol '$x'
  in sub dump_value at xxx/somelib.pm6 (somelib) line 3
  in block <unit> at ./client.pl6 line 8

以下是一些实验。他们都没有成功。

say ::("MY::$symbol")

say ::("OUR::$symbol")

say ::("OUTER::$symbol")

say ::("CLIENT::$symbol")
...

那么如何修复代码呢？

更新:

谢谢! CALLERS::($symbol)解决了我原来的问题。但在更复杂的情况下，编译器再次提示:

# somelib.pm6
unit module somelib;

sub dump_value(@symbols) is export {
    # output: 6
    say CALLERS::('$x');

    # error: No such symbol 'CALLERS::$x'    
    say @symbols.map({ CALLERS::($^id) } ) 
}

# client.pl6
#! /usr/bin/env perl6

use lib ".";
use somelib;

my $x = 6;
my $y = 8;

dump_value(<$x $y>);

再次更新:

使用 OUTER::CALLERS::($^id) .

一次又一次地更新:

在我将 'dump_value' 放入另一个 sub 后，它不再起作用了!

# somelib.pm6
unit module somelib;

sub dump_value(@symbols) is export {
    say @symbols.map({ OUTER::CALLERS::($^id) } )
}

sub wrapped_dump_value(@symbols) is export {
    dump_value(@symbols)
}

#! /usr/bin/env perl6

use lib ".";
use somelib;

my $x = 6;
my $y = 8;

# ouput: (6 8)
dump_value(<$x $y>);

# error: No such symbol 'OUTER::CALLERS::$x'
wrapped_dump_value(<$x $y>);

Answer 1

根据 the documentation :

An initial :: doesn't imply global. Here as part of the interpolation syntax it doesn't even imply package. After the interpolation of the ::() component, the indirect name is looked up exactly as if it had been there in the original source code, with priority given first to leading pseudo-package names, then to names in the lexical scope (searching scopes outwards, ending at CORE).

所以当你写 say ::("$symbol")在 dump_value()在 somelib包，它会先查找 $symbol在当前范围内，其值为 '$x'然后尝试查找 $x (也在当前范围内)，但变量 $x定义在调用者的词法范围内，所以你得到 No such symbol '$x'错误。

您可以引用由 $symbol 的值给出的调用者的词法符号。使用:

CALLER::MY::($symbol);  # lexical symbols from the immediate caller's lexical scope

或者

 CALLERS::($symbol); # Dynamic symbols in any caller's lexical scope

见 the package documentation page .