Perl6 中的 twigil 是什么？

Question

我正在阅读这本精彩的书 introduction to Perl6 并且遇到了一个相当有趣的术语：

Note the ! twigil means “this is private to the class”.
class ScoreKeeper {
  has %!player-points;
}

我知道 Perl5 中的内容 sigils are。但什么是 twigil？

attribute/variable 名字前面有两个印记只是一种奇特的说法吗？

Answer 1

似乎与变量作用域有关：

Twigils influence the scoping of a variable...

Twigil   Scope
------   ----------------------------------------------
none     Based only on declarator
*        Dynamic
!        Attribute (class member)
?        Compile-time variable
.        Method (not really a variable)
<        Index into match object (not really a variable)
^        Self-declared formal positional parameter
:        Self-declared formal named parameter
=        Pod variables
~        The sublanguage seen by the parser at this lexical spot

http://docs.raku.org/language/variables#Twigils

Answer 2

来自the documentation on twigils：

Attributes are variables that exist per instance of a class. They may be directly accessed from within the class via !:

class Point {
    has $.x;
    has $.y;

    method Str() {
        "($!x, $!y)"
    }
}

Note how the attributes are declared as $.x and $.y but are still accessed via $!x and $!y. This is because in Perl 6 all attributes are private and can be directly accessed within the class by using $!attribute-name. Perl 6 may automatically generate accessor methods for you though. For more details on objects, classes and their attributes see object orientation.

Public 属性有 . twigil，私有属性有 ! twigil。

class YourClass {
    has $!private;
    has @.public;

    # and with write accessor
    has $.stuff is rw;

    method do_something {
        if self.can('bark') {
            say "Something doggy";
        }
    }
}

Answer 3

设计文档S02 and S99都谈到了twigils。（强调我的）。

Ordinary sigils indicate normally scoped variables, either lexical or package scoped. Oddly scoped variables include a secondary sigil (a twigil) that indicates what kind of strange scoping the variable is subject to: [...]

所以它是一个次要印记或者更确切地说是一个第二个印记。声明 $*foo 不会声明 $foo.

my $*foo = 1;
say $foo;

这将产生 变量“$foo”未声明在...。

Perl6 中的 twigil 是什么？

What is a twigil in Perl6?

perl

terminology

raku