Как на самом деле работает анонимная функция case в Scala?
Ар Скала,
scala> val f1: ((Int, Int)) => Int = { case (a, b) => a + b }
f1: ((Int, Int)) => Int =
scala> val f2: (Int, Int) => Int = { case (a, b) => a + b }
f2: (Int, Int) => Int =
да ?!
scala> f1(1, 2)
res2: Int = 3
Хорошо...
scala> def takesIntInt2Int(fun: (Int, Int) => Int) = fun(100, 200)
takesIntInt2Int: (fun: (Int, Int) => Int)Int
scala> def takesTuple2Int(fun: ((Int, Int)) => Int) = fun(100, 200)
takesTuple2Int: (fun: ((Int, Int)) => Int)Int
scala> takesIntInt2Int(f2)
res4: Int = 300
scala> takesIntInt2Int(f1)
:10: error: type mismatch;
found : ((Int, Int)) => Int
required: (Int, Int) => Int
takesIntInt2Int(f1)
^
scala> takesTuple2Int(f1)
res6: Int = 300
scala> takesTuple2Int(f2)
:10: error: type mismatch;
found : (Int, Int) => Int
required: ((Int, Int)) => Int
takesTuple2Int(f2)
Правильно. А теперь посмотри на это!
scala> takesTuple2Int { case (a, b, c) => a + b + c }
:9: error: constructor cannot be instantiated to expected type;
found : (T1, T2, T3)
required: (Int, Int)
takesTuple2Int { case (a, b, c) => a + b + c }
^
scala> takesIntInt2Int { case (a, b, c) => a + b + c }
:9: error: constructor cannot be instantiated to expected type;
found : (T1, T2, T3)
required: (Int, Int)
takesIntInt2Int { case (a, b, c) => a + b + c }
Подобно,srsly? о_О оба результата вrequired: (Int, Int) ошибка.
Зачем тогда использоватьcase вообще в таких анонимных функциях?