Every language ever:
"You can't compare objects of type A and B"

Swift, on the other hand:
"main.swift:365:34: note: overloads for '==' exist with these partially matching parameter lists: (Any.Type?, Any.Type?), ((), ()), (Bool, B ool), (Character, Character), (Character.UnicodeScalarView.Index, Character.UnicodeScalarView.Index), (CodingUserInfoKey, CodingUserInfoKey ), (OpaquePointer, OpaquePointer), (AnyHashable, AnyHashable), (UInt8, UInt8), (Int8, Int8), (UInt16, UInt16), (Int16, Int16), (UInt32, UIn t32), (Int32, Int32), (UInt64, UInt64), (Int64, Int64), (UInt, UInt), (Int, Int), (AnyKeyPath, AnyKeyPath), (Unicode.Scalar, Unicode.Scalar ), (ObjectIdentifier, ObjectIdentifier), (String, String), (String.Index, String.Index), (UnsafeMutableRawPointer, UnsafeMutableRawPointer) , (UnsafeRawPointer, UnsafeRawPointer), (UnicodeDecodingResult, UnicodeDecodingResult), (_SwiftNSOperatingSystemVersion, _SwiftNSOperatingS ystemVersion), (AnyIndex, AnyIndex), (AffineTransform, AffineTransform), (Calendar, Calendar), (CharacterSet, CharacterSet), (Data, Data), (Date, Date), (DateComponents, DateComponents), (DateInterval, DateInterval), (Decimal, Decimal), (IndexPath, IndexPath), (IndexSet.Index, IndexSet.Index), (IndexSet.RangeView, IndexSet.RangeView), (IndexSet, IndexSet), (Locale, Locale), (Notification, Notification), (NSRange,

NSRange), (String.Encoding, String.Encoding), (PersonNameComponents, PersonNameComponents), (TimeZone, TimeZone), (URL, URL), (URLComponent s, URLComponents), (URLQueryItem, URLQueryItem), (URLRequest, URLRequest), (UUID, UUID), (DarwinBoolean, DarwinBoolean), (DispatchQoS, Disp atchQoS), (DispatchTime, DispatchTime), (DispatchWallTime, DispatchWallTime), (DispatchTimeInterval, DispatchTimeInterval), (Selector, Sele ctor), (NSObject, NSObject), (CGAffineTransform, CGAffineTransform), (CGPoint, CGPoint), (CGSize, CGSize), (CGVector, CGVector), (CGRect, C GRect), ((A, B), (A, B)), ((A, B, C), (A, B, C)), ((A, B, C, D), (A, B, C, D)), ((A, B, C, D, E), (A, B, C, D, E)), ((A, B, C, D, E, F), (A , B, C, D, E, F)), (ContiguousArray<Element>, ContiguousArray<Element>), (ArraySlice<Element>, ArraySlice<Element>), (Array<Element>, Array <Element>), (AutoreleasingUnsafeMutablePointer<Pointee>, AutoreleasingUnsafeMutablePointer<Pointee>), (ClosedRangeIndex<Bound>, ClosedRange Index<Bound>), (LazyDropWhileIndex<Base>, LazyDropWhileIndex<Base>), (EmptyCollection<Element>, EmptyCollection<Element>), (FlattenCollecti onIndex<BaseElements>, FlattenCollectionIndex<BaseElements>), (FlattenBidirectionalCollectionIndex<BaseElements>, FlattenBidirectionalColle ctionIndex<BaseElements>), (Set<Element>, Set<Element>), (Dictionary<Key, Value>.Keys, Dictionary<Key, Value>.Keys), ([Key : Value], [Key : Value]), (Set<Element>.Index, Set<Element>.Index), (Dictionary<Key, Value>.Index, Dictionary<Key, Value>.Index), (ManagedBufferPointer<Hea der, Element>, ManagedBufferPointer<Header, Element>), (Wrapped?, Wrapped?), (Wrapped?, _OptionalNilComparisonType), (_OptionalNilCompariso nType, Wrapped?), (LazyPrefixWhileIndex<Base>, LazyPrefixWhileIndex<Base>), (Range<Bound>, Range<Bound>), (CountableRange<Bound>, Countable Range<Bound>), (ClosedRange<Bound>, ClosedRange<Bound>), (CountableClosedRange<Bound>, CountableClosedRange<Bound>), (ReversedIndex<Base>, ReversedIndex<Base>), (_UIntBuffer<Storage, Element>.Index, _UIntBuffer<Storage, Element>.Index), (UnsafeMutablePointer<Pointee>, UnsafeMut ablePointer<Pointee>), (UnsafePointer<Pointee>, UnsafePointer<Pointee>), (_ValidUTF8Buffer<Storage>.Index, _ValidUTF8Buffer<Storage>.Index) , (Self, Other), (Self, R), (Measurement<LeftHandSideType>, Measurement<RightHandSideType>)"

"/path/to/my/file.swift:143:34: error: cannot convert return expression of type 'String.SubSequence' (aka 'Substring') to return type 'String'"

Ah yes, I love it when Substring isn't String

Why does Java not have operator overloads? Don't you just love doing A.add(B) all the time?