scala - Cannot modify Seq.head -

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i'm learning scala, , got confused seq.head.

scala> x = array(1, 2, 3) x: array[int] = [i@545e9f15  scala> x res64: array[int] = array(1, 2, 3)  scala> x(0) res65: int = 1  scala> x.head res66: int = 1  scala> x(0) += 1  scala> x.head += 1 <console>:13: error: value += not member of int        x.head += 1               ^  scala> x.head = 1 <console>:12: error: value head_= not member of scala.collection.mutable.arrayops[int]        x.head = 1          ^  scala>

seems there's implicit conventions happening beneath.

but scala api, type of array.head int (in case):

def head: t

so why can modify element?

the key difference in question between x(0) += 1 (which works), , x.head += 1 (which fails).

x(0) += 1 equivalent x(0) = x(0) + 1, syntaxic sugar x.update(0, x.apply(0) + 1). instruction increases value of x(0).

x.head returns , int, immutable, x.head += 1 fails.





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