小编jbr*_*htl的帖子

我想要一个接受只读列表的数据类:

data class Notebook(val notes: List<String>) {
}

但它也可以接受MutableList,因为它是一个子类型List.

例如,以下代码修改传入的列表:

fun main(args: Array<String>) {
    val notes = arrayListOf("One", "Two")
    val notebook = Notebook(notes)

    notes.add("Three")

    println(notebook)       // prints: Notebook(notes=[One, Two, Three])
}

有没有办法如何在数据类中执行传入列表的防御副本？

说我有3个perl文件.

run.pl

#!/usr/bin/perl
use strict;
use warnings;
use Common;

validate();    # no need of Common::validate()

Common.pm

package Common;

use strict;
use warnings;
use Exporter qw(import);
use Validator;

our @EXPORT = qw(validate inArray);

sub validate
{
    Validator::doSomething();
}

sub inArray
{
    print("HERE\n");
}

return 1;

Validator.pm

package Validator;

use strict;
use warnings;
use Common;

sub doSomething
{
    inArray();    # only Common::inArray() works here, why?
}

return 1;

运行时输出为: Undefined subroutine &Validator::inArray called at Validator.pm line 10.

如果我改变

sub doSomething
{
    inArray(); …