typescript Angular 2 OpaqueToken 与 Angular 4 InjectionToken
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Angular 2 OpaqueToken vs Angular 4 InjectionToken
提问by Estus Flask
InjectionTokenwas introduced in Angular 4 and OpaqueTokenwas marked as deprecated.
InjectionToken在 Angular 4 中引入OpaqueToken并被标记为已弃用。
According to the manual, it is supposed to be used as
根据手册，它应该用作
const anyToken = new InjectionToken('any');
for untyped token, and as
对于无类型标记，以及
const numberToken = new InjectionToken<number>('number');
for typed token.
用于键入令牌。
However, typed token still can be injected and used with different type when it is injected, TypeScript will be ok with this, won't it?
但是，typed token 仍然可以注入并在注入时与不同的类型一起使用，TypeScript 可以解决这个问题，不是吗？
constructor(@Inject(numberToken) any, @Inject(numberToken) string: string) { ... }
How is InjectionTokensupposed to benefit from TypeScript type system?
InjectionToken应该如何从 TypeScript 类型系统中受益？
Why was OpaqueTokendeprecated if there's no practical difference between those two?
OpaqueToken如果这两者之间没有实际区别，为什么会被弃用？
回答by Max Koretskyi
Based on the internal usage of InjectionToken, for example, here, I assume that InjectionTokengives you type checking benefit when getting a dependency through injectorinstance:
InjectionToken例如，基于 的内部用法，这里，我假设InjectionToken在通过injector实例获取依赖项时可以为您提供类型检查的好处：
import {Component, InjectionToken, Injector} from "@angular/core";
interface AppConfig {
name: string;
}
let APP_CONFIG = new InjectionToken<AppConfig>('app.config');
let appConfig: AppConfig = {name: 'Cfg'};
@Component({
...
providers: [{provide: APP_CONFIG, useValue: appConfig}]
})
export class TestComponent {
constructor(injector: Injector) {
const config = injector.get(APP_CONFIG);
config.s = 'd';
^^^^^ - Error:(14, 16) TS2339:Property 's' does not exist on type 'AppConfig'.
}
}
