我是否总是必须向 Tkx 的 -command 参数提供匿名子例程？

发布于 2024-08-28 21:39:29 字数 516 浏览 9 评论 0原文

我觉得有点奇怪，在为 Tkx 小部件指定 -command 参数时，我必须匿名包装定义的子例程。

TkDocs 教程的摘录演示了这一点：

my $cb = $frm->new_ttk__button ( -text => "Calculate",
                                 -command => sub {calculate();}  );

sub calculate {
   $meters = int(0.3048*$feet*10000.0+.5)/10000.0 || '';
}

为什么我写的时候它不起作用<代码>-命令=> &calculate() 或 -command => \&计算()？

原文

I find it a bit weird that I have to wrap defined subroutines anonymously when specifying the -command argument for Tkx widgets.

An excerpt from a TkDocs tutorial demonstrates this:

my $cb = $frm->new_ttk__button ( -text => "Calculate",
                                 -command => sub {calculate();}  );

sub calculate {
   $meters = int(0.3048*$feet*10000.0+.5)/10000.0 || '';
}

Why doesn't it work when I write -command => &calculate() or -command => \&calculate()?

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著墨染雨君画夕 2024-09-04 21:39:29

你的语法不太正确。您的示例调用子例程（& 绕过任何原型）并传递返回值 (&calculate()) 或对其的引用 (\ &calculate()) 到 -command 选项。您想要分配对子例程本身的引用，可以通过以下方式完成：

-command => \&calculate

注意缺少尾随括号。另请注意，您不能以这种方式传递参数。如果你想这样做，你需要将调用包装在匿名子例程中：

-command => sub { calculate(12) }

或者向选项传递 ARRAY 引用而不是 CODE 引用：

-command => [\&calculate, 12]

这两种形式之间存在细微差别，如果您使用变量而不是文字，这一点很重要价值。

-command => sub { calculate($x) }  # creates a closure over $x
-command => [\&calculate, $x]      # makes a copy of $x

使用第一种形式对 $x 的更改将在调用命令时可见。在第二种形式下，他们不会；每次调用都会看到创建绑定时的值。两种形式都很有用；您只需要在决定使用哪个时做出良好的判断即可。

You don't have the syntax quite right. Your examples call the subroutine (the & bypasses any prototypes) and passes either the return value (&calculate()) or a reference to it (\&calculate()) to the -command option. You want to assign a reference to the subroutine itself, which you can do via:

-command => \&calculate

Note the lack of trailing parentheses. Also note that you can't pass arguments this way. If you want to do that you need to either wrap the call in an anonymous subroutine:

-command => sub { calculate(12) }

or pass the option an ARRAY reference instead of a CODE reference:

-command => [\&calculate, 12]

There's a subtle difference between the two forms that's important if you use a variable instead of a literal value.

-command => sub { calculate($x) }  # creates a closure over $x
-command => [\&calculate, $x]      # makes a copy of $x

Using the first form changes to $x will be visible when the command is invoked. Under the second form they won't be; each invocation will see the value at the moment the binding was created. Both forms are useful; you just need to exercise good judgment when deciding which to use.

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