如何将类属性声明为类名的联合？

我正在阅读电子表格寻找不同的结构。当我使用 Moose 尝试以下操作时，它似乎做了我想要的事情。我可以创建不同类型的对象，将其分配给找到的成员 并转储 Cell 实例以供审查。

package Cell
{
  use Moose;
  use Moose::Util::TypeConstraints;
  use namespace::autoclean;

  has 'str_val'    => ( is => 'ro', isa => 'Str', required => 1 );
  has 'x_id'       => ( is => 'ro', isa => 'Str', ); # later required => 1 );
  has 'color'      => ( is => 'ro', isa => 'Str', );
  has 'border'     => ( is => 'ro', isa => 'Str', );
  has 'found'      => ( is => 'rw', isa => 'Sch_Symbol|Chip_Symbol|Net', );
  1;
}

如果我尝试在 Perl 6 中执行相同的操作，它将无法编译。

class Cell {
  has Str $.str_val              is required;
  has Str $.x_id                 is required;
  has Str $.color;
  has Str $.border;
  has Sch_Symbol|Chip_Symbol|Net $.found is rw
}

Malformed has
at C:\Users\Johan\Documents/moose_sch_3.pl6:38
------>   has Sch_Symbol'<'HERE'>'|Chip_Symbol|Net $.found is rw

我怎样才能在 Perl 6 中做到这一点？

您可能希望他们扮演共同角色并将其指定为类型

role Common {}
class Sch-Symbol does Common {…}
…

class Cell {
  …
  has Common $.found is rw;
}

或者你将不得不使用where约束

class Cell {
  …
  has $.found is rw where Sch-Symbol|Chip-Symbol|Net;
}

您还可以创建一个子集来包装where约束。

subset Common of Any where Sch-Symbol|Chip-Symbol|Net;

class Cell {
  …
  has Common $.found is rw;
}

请注意，一个where约束比使用公共角色慢。