scala - Scala 中 int 的 += 方法在哪里

Question

+=(或任何赋值运算符)是 Scala 中 Int 类型的方法。

例如，

var x=5
x+=1

在这里，只有当它是一个变量时，我才能使用 += 方法。

我做不到，

5+=1

Scala 编译器是否将此方法视为特例？

为什么它在 scala.Int 类中不可用？

Answer 1

没有+=方法，扩展为 x = x + 1由编译器。这在 specification 中有详细说明:

6.12.4 赋值运算符

Let's consider an assignment operator such as += in an infix operation l += r, where l, r

are expressions. This operation can be re-interpreted as an operation which corresponds to the assignment

l = l + r

except that the operation's left-hand-side l is evaluated only once.

The re-interpretation occurs if the following two conditions are fulfilled.

1. The left-hand-side l does not have a member named +=, and also cannot be converted by an implicit conversion to a value with a member named +=.

2. The assignment l = l + r is type-correct. In particular this implies that l refers to a variable or object that can be assigned to, and that is convertible to a value with a member named +.