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kujon opened this issue Sep 18, 2017 · 2 comments
Closed

Generic constraints are sometimes lost #18552

kujon opened this issue Sep 18, 2017 · 2 comments
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@kujon
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kujon commented Sep 18, 2017

TypeScript Version: 2.4.2

Code

type A = {
    foo: number;
    bar: string;
};

class Component<T> {
    props: T;
    constructor(props: T) {
        this.props = props;
    }
    render(): Component<T> | null {
        return null;
    };
}

const exampleHOC = <T extends A>(
    WrappedComponent: Component<T>
) => {
    return class ExampleHOC extends Component<T> {
        render() {
            /** Rest types may only be created from object types.  */
            const { foo, ...rest } = this.props;

            return new Component(this.props);
        }
    }
};

Expected behavior:
The code above compiles.

Actual behavior:
Rest types may only be created from object types. error message is shown, which leads me to believe that at the time of destructuring the props, T doesn't have any constraints applied to it.

@mhegazy
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mhegazy commented Sep 18, 2017

The type of this.props is T which is a genric type. rest/spread is not supported on higher order types yet. see #10727 and #13470

@mhegazy mhegazy added the Duplicate An existing issue was already created label Sep 18, 2017
@mhegazy
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mhegazy commented Oct 2, 2017

Automatically closing this issue for housekeeping purposes. The issue labels indicate that it is unactionable at the moment or has already been addressed.

@mhegazy mhegazy closed this as completed Oct 2, 2017
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