I am currently working with angular 5 and ionic 3. I have defined an interface:
export interface IAny {
getDataSource: Observable<any>;
}
Components that implement this interface must have the following method:
getDataSource () {
return Observable.of(['Item1', 'Item2', 'Item3'] as any)
};
This method is expected to return various types of dataSources, such as a simple array of strings, an array of objects, or even a single object.
Is it feasible to achieve this functionality?
Yes, it is indeed possible to achieve the desired outcome without necessitating the casting of the array to any.
In the provided example, if you refrain from doing so, your function will be classified as type
() => Observable<string>() => Observable<any>, the type specified within the interface definition.
To illustrate further:
let a: () => Observable<any>;
let b: () => Observable<string>;
You can then proceed to execute:
a = b;
This seamless compatibility arises because in TypeScript, any is inherently compatible with all types available.
If you're looking for ways to accomplish this task, consider the following options:
return Observable.of<any>(['Item1', 'Item2', 'Item3'])
return Observable.of(['Item1', 'Item2', 'Item3']) as any
return Observable.of(['Item1', 'Item2', 'Item3']) as Observable<any> // Use this for code completion
Any of these methods should do the trick. Simply substitute your desired type in place of any.
Also, it's important to define your interface like this:
export interface IAny {
getDataSource(): Observable<any>;
}
Remember, you are declaring a function here, not a variable.
As suggested by @nicowernli, if you want more flexibility with typing on the fly, consider defining your interface and functions with generic types:
export interface IAny {
getDataSource<T>(): Observable<T>;
}
getDataSource<T>() {
return Observable.of(['Item1', 'Item2', 'Item3'] as any)
};
For those who, like myself, prefer to minimize the usage of the 'any' type (and avoid any necessary castings), consider creating a Type Alias specifically for your value.
An example implementation could be as follows:
// Define the potential return value types
type DataSourceType = Array<string> | Array<object> | object;
You can learn more about Type Aliases in the official TypeScript documentation.
To further refine this approach, you may also replace the generic object type with a custom type of your own.
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