Haxe中的常数 [英] Constants in Haxe

问题描述

如何在Haxe中创建公共常量?我只需要AS3中很好的旧 const 的类似物:

How do you create public constants in Haxe? I just need the analog of good old const in AS3:

public class Hello
{
     public static const HEY:String = "hey";
}

推荐答案

在Haxe中声明常量的通常方法是使用 static 和 inline 修饰符.

The usual way to declare a constant in Haxe is using the static and inline modifiers.

class Main {
    public static inline var Constant = 1;

    static function main() {
        trace(Constant);
        trace(Test.Constant);
    }
}

如果您有一组相关的常数，通常使用枚举摘要 .枚举摘要的值隐式地为 static 和 inline .

If you have a group of related constants, it can often make sense to use an enum abstract. Values of enum abstracts are static and inline implicitly.

请注意，仅允许使用基本类型( Int ， Float ， Bool )和 String 成为 inline ，对于其他人，它将因以下错误而失败:

Note that only the basic types (Int, Float, Bool) as well as String are allowed to be inline, for others it will fail with this error:

内联变量初始化必须为常数

Inline variable initialization must be a constant value

幸运的是，Haxe 4引入了 final 关键字，在这种情况下非常有用:

Luckily, Haxe 4 has introduced a final keyword which can be useful for such cases:

public static final Regex = ~/regex/;

但是， final 仅防止重新分配，它不会使类型不可变.因此，仍然有可能从 static final Values = [1、2、3]; 之类的值中添加或删除值.

However, final only prevents reassignment, it doesn't make the type immutable. So it would still be possible to add or remove values from something like static final Values = [1, 2, 3];.

对于数组的特定情况，Haxe 4引入了 haxe.ds.ReadOnlyArray 允许使用恒定"列表(假设您不使用强制转换或反射方法来解决此问题):

For the specific case of arrays, Haxe 4 introduces haxe.ds.ReadOnlyArray which allows for "constant" lists (assuming you don't work around it using casts or reflection):

public static final Values:haxe.ds.ReadOnlyArray<Int> = [1, 2, 3];

Values = []; // Cannot access field or identifier Values for writing
Values.push(0); // haxe.ds.ReadOnlyArray<Int> has no field push

即使这是特定于阵列的解决方案，也可以将相同的方法应用于其他类型. ReadOnlyArray< T> 只是创建的抽象类型通过执行以下操作创建只读的视图":

Even though this is an array-specific solution, the same approach can be applied to other types as well. ReadOnlyArray<T> is simply an abstract type that creates a read-only "view" by doing the following:

• 它包装 Array< T>
• 它使用 @:forward 来仅公开不更改数组的字段，例如 length 和 map()
• 它允许隐式强制转换 来自Array< T>

• it wraps Array<T>
• it uses @:forward to only expose fields that don't mutate the array, such as length and map()
• it allows implicit casts from Array<T>

此处.

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