亲爱的斯卡拉,
scala> val f1: ((Int, Int)) => Int = { case (a, b) => a + b }
f1: ((Int, Int)) => Int = <function1>
scala> val f2: (Int, Int) => Int = { case (a, b) => a + b }
f2: (Int, Int) => Int = <function2>
啊?!
scala> f1(1, 2)
res2: Int = 3
好的...
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)
<console>:10: error: type mismatch;
found : ((Int, Int)) => Int
required: (Int, Int) => Int
takesIntInt2Int(f1)
^
scala> takesTuple2Int(f1)
res6: Int = 300
scala> takesTuple2Int(f2)
<console>:10: error: type mismatch;
found : (Int, Int) => Int
required: ((Int, Int)) => Int
takesTuple2Int(f2)
正确的。现在,看看这个!
scala> takesTuple2Int { case (a, b, c) => a + b + c }
<console>: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 }
<console>:9: error: constructor cannot be instantiated to expected type;
found : (T1, T2, T3)
required: (Int, Int)
takesIntInt2Int { case (a, b, c) => a + b + c }
像,srsly?o_O 两者都导致required: (Int, Int)
错误。
那么为什么要case
在这样的匿名函数中使用呢?