// I know you meant it to be exaggerated, but I still think this is the better approach in practice:

enum ClassError: Error {
    case propertyNotFound(name: String)
    case typeMismatch(propertyName: String)
}

class Foo {
    var properties: [(String, Any)] = []
    private func validateValue(_ value: Any, for property: String) throws { // Note that I pass the name just for the error; that's ok IMO
        // ... some logic
        throw ClassError.typeMismatch(propertyName: property)
    }

    private func validateProperty(name: String, value: Any) throws {
        if true {
            throw ClassError.propertyNotFound(name: name)
        }
        try validateValue(value, for: name) // Don't need to wrap
    }

    func validate(name: String) throws { // should only throw a ClassError
        for (name, value) in self.properties {
            try validateProperty(name: name, value: value)
        }
    }
}