SwiftUI: Fatal error: Duplicate keys of type 'SOMETYPE' were found in a Dictionary

[cukr]

From Hashable documentation:

Hashing a value means feeding its essential components into a hash function, represented by the Hasher type. Essential components are those that contribute to the type’s implementation of Equatable. Two instances that are equal must feed the same values to Hasher in hash(into:), in the same order.

your code:

    static func == (lhs: Vorlesung, rhs: Vorlesung) -> Bool {
        let result = lhs.subject.compare(rhs.subject) == .orderedSame
        return result
    }
    func hash(into hasher: inout Hasher) {
        hasher.combine(vID) // UUID
    }

Currently your hash and == are using completely different properties, which leads to conflict between them. Are two Vorlesung with the same subject but different vID equal to each other, or not? According to == they are equal, but according to hash they are not. We need to fix that

You need to decide what makes two Vorlesung the same, and use these properties in both == and hash. Usually in a struct it's all of the properties, and that's handled by the autogenerated implementation