将一般类型转换为具体类型时出错 [英] Error casting a generic type to a concrete one

问题描述

我具有以下TypeScript函数：

I have the following TypeScript function:

add(element: T) {
 if (element instanceof class1) (<class1>element).owner = 100;
}

问题是我遇到以下错误：

the problem is that I'm getting the following error:

错误TS2012：无法将'T'转换为'class1'

error TS2012: Cannot convert 'T' to 'class1'

有什么想法吗？

推荐答案

不能保证您的类型兼容，因此您必须进行双重转换，因为每个以下内容...

There is no guarantee that your types are compatible, so you have to double-cast, as per the following...

class class1 {
    constructor(public owner: number) {

    }
}

class Example<T> {
    add(element: T) {
        if (element instanceof class1) {
             (<class1><any>element).owner = 100;
         }
    }
}

当然，如果您使用泛型类型约束，您可以删除强制类型转换和检查...

Of course, if you use generic type constraints, you could remove the cast and the check...

class class1 {
    constructor(public owner: number) {

    }
}

class Example<T extends class1> {
    add(element: T) {
        element.owner = 100;
    }
}

这是使用 class1 作为约束，但是您可能决定使用任何类都必须满足才能有效的接口-例如，它必须具有名为 owner 的属性。类型为数字。

This is using class1 as the constraint, but you might decide to use an interface that any class has to satisfy to be valid - for example it must have a property named owner of type number.

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