scala 类型不匹配错误，需要 GenTraversableOnce[?]
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scala type mismatch error, GenTraversableOnce[?] required
提问by Vadim Samokhin
Why does this code result in the compilation error
为什么这段代码会导致编译错误
type mismatch; found : (Int, Char) required: scala.collection.GenTraversableOnce[?]
类型不匹配; found : (Int, Char) required: scala.collection.GenTraversableOnce[?]
?
?
val n = Map(1 -> 'a', 4 -> 'a')
def f(i: Int, c: Char) = (i -> c)
n.flatMap (e => f(e._1, e._2))
采纳答案by Tomasz Nurkiewicz
Use map()instead:
使用map()来代替：
n.map (e => f(e._1, e._2))
flatMap()assumes you are returning a collection of values rather than a single element. Thus these would work:
flatMap()假设您返回的是一组值而不是单个元素。因此，这些将起作用：
n.flatMap (e => List(f(e._1, e._2))
n.flatMap (e => List(f(e._1, e._2), f(e._1 * 10, e._2)))
The second example is interesting. For each [key, value] pair we return two pairs which are then merged, so the result is:
第二个例子很有趣。对于每个 [key, value] 对，我们返回两对然后合并，因此结果是：
Map(1 -> a, 10 -> a, 4 -> a, 40 -> a)
