是否可以在 TypeScript 中声明和调用函数字典？

Question

我正在做一些重构，想知道是否可以声明和初始化工厂函数字典，以枚举器为键，这样它就可以用作工厂函数的查找，然后可以叫什么？或者，或者，我是否在这方面走错了路并且错过了更优雅的解决方案。我按照 this answer 声明并初始化了一个类型化的字典，但我不确定我是否声明了签名正确，例如键是一个数字，值是一个函数。我已将我的代码简化为一个非常通用的示例 - 我知道它相当做作，但这样做的意图更加清晰。

// Types are enumerated as I have several different lists of types which I'd like to
// implement as an array of enumerators
enum ElementType {
    TypeA,
    TypeB,
    TypeC
}

// Here, I'm trying to declare a dictionary where the key is a number and the value is a
// function
var ElementFactory: { [elementType: number]: () => {}; };

// Then I'm trying to declare these factory functions to return new objects
ElementFactory[ElementType.TypeA] = () => new ElementOfTypeA();
ElementFactory[ElementType.TypeB] = () => new ElementOfTypeB();
ElementFactory[ElementType.TypeC] = () => new ElementOfTypeC();

// And finally I'd like to be able to call this function like so such that they return
// instantiated objects as declared in the code block above
var a = ElementFactory[ElementType.TypeA]();
var b = ElementFactory[ElementType.TypeB]();
var c = ElementFactory[ElementType.TypeC]();

Answer 1

您的代码大部分是正确的，这种方法也行得通，但有一点可以改进：

// Here, I'm trying to declare a dictionary where the key is a number and the value is a
// function
var ElementFactory: { [elementType: number]: () => {}; };

在类型定义中，() => {} 表示 "a function that takes zero parameters and returns a {}"。您可以在此处修改 return 类型以使其更具体，但遗憾的是，无论何时调用这些工厂函数，您仍然需要手动表达 returned 值的类型。例如，您可以这样做：

type AnyElementType = ElementOfTypeA | ElementOfTypeB | ElementOfTypeC;

var ElementFactory: { [elementType: number]: () => AnyElementType; };

...

// this type declaration will not work
var a: ElementOfTypeA = ElementFactory[ElementType.TypeA]();

// but these will
var b = <ElementOfTypeB>ElementFactory[ElementType.TypeB]();
var c = ElementFactory[ElementType.TypeC]() as ElementOfTypeC;

是否可以在 TypeScript 中声明和调用函数字典？

Is it possible to declare and call a dictionary of functions in TypeScript?

dictionary

enumeration

factory

function

typescript