/**
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Create a type that makes the given keys optional. The remaining keys are kept as is. The sister of the `SetRequired` type.
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Use-case: You want to define a single model where the only thing that changes is whether or not some of the keys are optional.
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@example
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```
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import {SetOptional} from 'type-fest';
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type Foo = {
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a: number;
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b?: string;
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c: boolean;
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}
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type SomeOptional = SetOptional<Foo, 'b' | 'c'>;
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// type SomeOptional = {
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// a: number;
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// b?: string; // Was already optional and still is.
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// c?: boolean; // Is now optional.
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// }
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```
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*/
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export type SetOptional<BaseType, Keys extends keyof BaseType = keyof BaseType> =
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// Pick just the keys that are not optional from the base type.
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Pick<BaseType, Exclude<keyof BaseType, Keys>> &
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// Pick the keys that should be optional from the base type and make them optional.
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Partial<Pick<BaseType, Keys>> extends
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// If `InferredType` extends the previous, then for each key, use the inferred type key.
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infer InferredType
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? {[KeyType in keyof InferredType]: InferredType[KeyType]}
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: never;
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