Haxe摘要-使用@：from时可以隐式转换数组吗？

问题描述

我正在尝试将一种类型的数组视为另一种（抽象）类型的数组。当我使用抽象的基础类型时，它可以正常工作。但是，当我尝试使用另一种类型（使用 @：from 关键字定义）进行隐式转换时，出现构建失败。

I'm attempting to treat an array of one type as an array of another (abstract) type. It works fine when I use the underlying type of the abstract. But when I attempt implicit conversion using another type (defined using @:from keyword), I get a build failure.

如果我使用显式的 cast ，它可以工作，但是我想知道-有什么办法解决/

It works if I use an explicit cast, but I'm wondering - is there any way around this / something I'm missing?

在以下示例中，出现构建失败 Array< Int>应该是Array< StringAbstract>

In the example below, I get the build failure Array<Int> should be Array<StringAbstract>

class Test {
    static function main() {
        var test:String = "Hello World";
        print(test); //this works

        var testArr:Array<String> = ["Hello", "World"];
        printArray(testArr); //this works (using underlying type)

        var testInt:Int = 10;
        print(testInt); //this works

        var testIntArr:Array<Int> = [1, 2, 3];
        printArray(cast testIntArr);  //this works (explicit cast)
        printArray(testIntArr);  //build failure (using @:from)
    }

    static function print(s:StringAbstract) {
        trace(s);
    }

    static function printArray(arr:Array<StringAbstract>) {
        trace(arr);
    }
}

abstract StringAbstract(String) from String to String {
    inline function new(s:String) {
        this = s;
    }

    @:from
    static public function fromInt(i:Int) {
        return new StringAbstract(Std.string(i));
    }
}

---

跟进

根据Gama11和Justinfront的建议，我定义了一个摘要，将数组转换为我的抽象类型的数组。但是，现在我遇到了另一个问题-声明@：from函数后，它就会破坏以前可以正常工作的代码。

Taking suggestions from Gama11 and Justinfront, I defined an abstract to convert arrays to arrays of my abstract type. But now I'm running into a different issue - as soon as I declare a @:from function, it breaks code that used to work.

具体地说，我以前能够使用隐式转换为抽象的混合类型调用我的函数（例如 printArray（[1， 2，3]）; ）。

Specifically, I used to be able to call my function with "mixed" types that were implicitly converted to the abstract (e.g. printArray([1, "2", 3]);).

但是，一旦我添加了 @：from 函数即可从其他类型的数组（ Array< Int> ），该功能中断了，并出现错误仅当类型强制为Array< Dynamic>时，才允许使用混合类型的数组。 。

But as soon as I added a @:from function to convert from a different type of array (Array<Int> in this case), that functionality broke, with the error Arrays of mixed types are only allowed if the type is forced to Array<Dynamic>.

好奇是否有人知道原因（例如：）。

Curious if anyone knows why this would be (example: https://try.haxe.org/#65D03).

class Test {
    static function main() {
        var testMixedArr:Array<StringAbstract> = [1, "2", 3];
        printArray(testMixedArr); //this works
        printArray([1, "2", 3]); //this doesn't work, unless I remove "fromIntArray" function
    }

    static function printArray(arr:StringAbstractArray) {trace(arr);}
}


abstract StringAbstractArray(Array<StringAbstract>) from Array<StringAbstract> to Array<StringAbstract> {
    inline function new(s:Array<StringAbstract>) {
        this = s;
    }

    @:from
    static public function fromIntArray(intArr:Array<Int>) {
        return new StringAbstractArray(Lambda.array( Lambda.map( intArr, function(i: Int):StringAbstract {
            return i; } )));
    }
}

推荐答案

解决此问题的唯一方法是定义一个显式的 @：from 函数，该函数采用 Array< Int> 。 《 Haxe手册》 中对此进行了解释。它有一个很好的例子，说明这种情况下的强制转换如何导致运行时执行不安全的代码（而不是被编译器捕获）。

The only way around this is to define an explicit @:from function that takes an Array<Int>. The reason for this is explained in the Variance section of the Haxe Manual. It has a good example of how casting in this case can lead to unsafe code being executed at runtime (rather than being caught by the compiler).

这篇关于Haxe摘要-使用@：from时可以隐式转换数组吗？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！