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    Type Alias IsUnion<U>

    IsUnion: IsUnionImpl<U, U>

    Checks if a given type U is a union type (contains more than one distinct type member).

    It works by distributing over the potential union members of U and comparing the original type U with each distributed member M. If U is a union, there will be at least one M for which TypeEq<U, M> is false, causing the result for that branch to be true. The final result becomes true if any branch evaluates to true. If U is not a union, M will be the same as U, TypeEq<U, M> will be true, and the result will be false.

    Note: never, any, and unknown are not considered unions by this type.

    Type Parameters

    • U

      The type to check.

    true if U is a union type, false otherwise.

    type T1 = IsUnion<string | number>; // true
    type T2 = IsUnion<string>; // false
    type T3 = IsUnion<string | string>; // false (simplifies to string)
    type T4 = IsUnion<never>; // false
    type T5 = IsUnion<any>; // false
    type T6 = IsUnion<unknown>; // false
    type T7 = IsUnion<true | false>; // true (boolean)
    type T8 = IsUnion<boolean>; // true (equivalent to true | false)

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