30 lines
1.5 KiB
Plaintext
30 lines
1.5 KiB
Plaintext
import type {IsUnknown} from './is-unknown';
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/**
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Create a function type with a return type of your choice and the same parameters as the given function type.
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Use-case: You want to define a wrapped function that returns something different while receiving the same parameters. For example, you might want to wrap a function that can throw an error into one that will return `undefined` instead.
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@example
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```
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import type {SetReturnType} from 'type-fest';
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type MyFunctionThatCanThrow = (foo: SomeType, bar: unknown) => SomeOtherType;
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type MyWrappedFunction = SetReturnType<MyFunctionThatCanThrow, SomeOtherType | undefined>;
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//=> type MyWrappedFunction = (foo: SomeType, bar: unknown) => SomeOtherType | undefined;
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```
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@category Function
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*/
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export type SetReturnType<Function_ extends (...arguments_: any[]) => any, TypeToReturn> =
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// Just using `Parameters<Fn>` isn't ideal because it doesn't handle the `this` fake parameter.
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Function_ extends (this: infer ThisArgument, ...arguments_: infer Arguments) => any ? (
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// If a function did not specify the `this` fake parameter, it will be inferred to `unknown`.
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// We want to detect this situation just to display a friendlier type upon hovering on an IntelliSense-powered IDE.
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IsUnknown<ThisArgument> extends true ? (...arguments_: Arguments) => TypeToReturn : (this: ThisArgument, ...arguments_: Arguments) => TypeToReturn
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) : (
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// This part should be unreachable, but we make it meaningful just in case…
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(...arguments_: Parameters<Function_>) => TypeToReturn
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);
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