porting - "Illegally post-declared types"带循环类定义

Question

乐堂版本 2020.01

这不编译。

use v6;

class N1 {}
class T1 {}

class G1 {
    has @.g is required where A1|Q1;
}

class Q1 {
    has $.q is required where N1|T1|G1;
}

class A1 {
    has Q1 @.a is required;
}

===SORRY!=== Error while compiling …
Illegally post-declared types:
    A1 used at line 7
    Q1 used at line 7

我认为仅在 G1 之前声明标识符会帮助我，但这也失败了:

===SORRY!=== Error while compiling …
Too late for unit-scoped class definition;
Please use the block form.
…:6
------> class A1;⏏ class Q1;

我如何使它工作？

Answer 1

您可以，但您需要将类定义为 stub 。

class A { }

只会定义一个空类。然而:

class A { ... }   # note the yadayadayada

将定义一个 stub 。所以补充:

class A1 { ... }
class Q1 { ... }

到您的代码顶部，应该可以解决问题。