围绕变量的花括号 [英] Curly braces surrounding variable

问题描述

我有一段代码，我想弄清楚，我什至不知道它的语法是否正确(我猜是练习的一部分！)

I have this piece of code that I'm trying to get my head around, I don't even know if its syntactically correct (part of the exercise I guess!)

%{$records}

大括号是什么意思?我见过同样的情况，但使用 @ 运算符而不是 $ 如果这有所不同.

What do the curly braces signify? I've seen the same case but with a @ operator used instead of the $ if that makes a difference.

谢谢各位！

推荐答案

使用参考" perlref 文档的部分解释.

2. 在您将标识符(或标识符链)作为变量或子例程名称的一部分放置的任何地方，您都可以用返回正确类型引用的 BLOCK 替换标识符.换句话说，前面的例子可以这样写:

2. Anywhere you’d put an identifier (or chain of identifiers) as part of a variable or subroutine name, you can replace the identifier with a BLOCK returning a reference of the correct type. In other words, the previous examples could be written like this:

   $bar = ${$scalarref};
   push(@{$arrayref}, $filename);
   ${$arrayref}[0] = "January";
   ${$hashref}{"KEY"} = "VALUE";
   &{$coderef}(1,2,3);
   $globref->print("output\n"); # iff IO::Handle is loaded

在您的情况下，$records 必须是对哈希的引用(因为最外面的 %)，{$records} 是返回引用的块，%{$records} 给出原始哈希值.

In your case, $records must be a reference to a hash (because of the outermost %), {$records} is a block that returns the reference, and %{$records} gives the original hash.

花括号包围一个真正的块.事实上，你可以用

The curly braces surround a bona fide block. In fact, you could replace the code above with

%{ if ($records) { $records } else { $default_records } }

但正如文档前面所指出的，即使是您问题中的较短版本也可以简化.

But even the shorter version from your question could be simplified, as pointed out earlier in the documentation.

1. 在您将标识符(或标识符链)作为变量或子例程名称的一部分放置的任何地方，您都可以将标识符替换为包含正确引用的简单标量变量类型:

1. Anywhere you’d put an identifier (or chain of identifiers) as part of a variable or subroutine name, you can replace the identifier with a simple scalar variable containing a reference of the correct type:

   $bar = $$scalarref;
   push(@$arrayref, $filename);
   $$arrayref[0] = "January";
   $$hashref{"KEY"} = "VALUE";
   &$coderef(1,2,3);
   print $globref "output\n";

因为 $records 是一个简单的标量，%$records 是底层哈希.

Because $records is a simple scalar, %$records is the underlying hash.

如果 $records 是对数组的引用，则取消引用它的语法将是 @$records 或 @{$records}.

If instead $records were a reference to an array, the syntax for dereferencing it would be @$records or @{$records}.

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