从“执行"位置的类中的 AT-POS 方法(而不是代理实例)返回“原始"标量容器? [英] Returning a 'raw' scalar container from AT-POS method (rather than a Proxy instance) in a class that 'does' Positional?

问题描述

我正在尝试实现一个执行"Positional 的类，该类还允许我通过分配给 AT-POS 方法返回的结果来更新其值.最终，我能够编造以下按预期工作的类:

I'm attempting to implement a class that 'does' Positional that also allows me to update its values by assigning to the result returned by the AT-POS method. Eventually, I was able to concoct the following class that works as intended:

class Test does Positional
{
    has $.slot_1 is rw = 12;
    has $.slot_2 is rw = 24;

    method AT-POS(\position)
    {
        my $t = self;

        return-rw Proxy.new:

            FETCH => method ()
            {
                position % 2 ?? $t.slot_1 !! $t.slot_2
            },

            STORE => method ($v)
            {
                if position % 2
                {
                    $t.slot_1 = $v
                }
                else
                {
                    $t.slot_2 = $v
                }
            }
    }
}

my $test = Test.new;

die unless $test[2] == 24;

die unless $test[5] == 12;


$test[7] = 120;

die unless $test[2] == 24;

die unless $test[5] == 120;


$test[10] = 240;

die unless $test[2] == 240;

die unless $test[5] == 120;

是否有可能以某种方式(并且:简单地)返回绑定到 $!slot_1(或 $!slot_2)的 containerTest 类的实现?

Would it be possible to somehow (and: simply) return the container bound to $!slot_1 (or $!slot_2) inside the Test class implementation?

在我发现使用 Proxy 实例之前，我尝试 return(和 return-rw)表达式 position 的结果% 2 ??$!slot_1.VAR !!$!slot_2.VAR，因为我的印象是 VAR 方法让我可以访问底层容器，希望我可以简单地return 它.这并没有真正起作用，我还不明白为什么:我怀疑它以某种方式被强制恢复为某个值?

Before I discovered the use of Proxy instances I attempted to return (and return-rw) the result of expression position % 2 ?? $!slot_1.VAR !! $!slot_2.VAR, because I'm under the impression that the VAR method gives me access to the underlying container, in the hope that I can simply return it. That didn't really work, and I do not understand why yet: I suspect it somehow gets coerced back to a value somehow?

换句话说:在这种特殊情况下，是否可以简化我的 AT-POS 实现?

So in other words: is it possible to simplify my AT-POS implementation in this particular situation?

谢谢，

问候，

雷蒙德.

推荐答案

假设您不想要slot_1"的访问器和slot_2"，如果我正确理解了这个问题，这将是我的实现.我不会称它为 Test 类，因为这会干扰用于测试的 Test 类.

Assuming you do not want accessors for "slot_1" and "slot_2", and if I understand the question correctly, this would be my implementation. I wouldn't call it a Test class, as that would interfere with the Test class that is used for testing.

class Foo {
    has @elements = 24, 12;

    method AT-POS(Int:D $pos) is raw {
        @elements[$pos % 2]
    }
}

my $f = Foo.new;
say $f[2];  # 24
say $f[5];  # 12

$f[2] = 666;
say $f[4];  # 666

注意数组中的默认值已经改变了顺序，这是为了保持AT-POS中的算术简单.

Note that the defaults in the array have changed order, that's to keep the arithmetic in AT-POS simple.

还要注意定义中的is rawAT-POS 方法:它将确保在返回值时不会发生去容器化.这允许您只分配给 $f[2] 返回的任何内容.

Also note the is raw in the definition of the AT-POS method: it will ensure that no de-containerization will take place when returning a value. This allows you to just assign to whatever $f[2] returns.

希望这是有道理的！

另外:Array::Agnostic 模块可能对您感兴趣，直接使用，或用作灵感来源.

Also: the Array::Agnostic module may be of interest for you, to use directly, or to use as a source of inspiration.

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