为什么在Go中不能使用add运算符进行元组分配？ [关闭]

Question

According to the Golang language syntax specification:

Assignment = ExpressionList assign_op ExpressionList .

assign_op = [ add_op | mul_op ] "=" .

furthermore:

A tuple assignment assigns the individual elements of a multi-valued operation to a list of variables.

However, when trying to compile the following code:

package main

func addOne(a, b int) (int, int) {
    return a+1, b+1
}

func main() {
    var a, b int
    a, b += addOne(a, b)
}

the compiler complains with:

syntax error: unexpected +=, expecting := or = or comma

I'm aware temporary variables can work around this. E.g.

aTemp, bTemp := addOne(a, b)
a += aTemp
b += bTemp

However, it seems like something the language says it supports.

Is this a bug in the compiler? Have I missed something in the language?

Answer 1

+= is an assignment operation, not a simple assignment. The spec says explicitly:

An assignment operation x op= y where op is a binary arithmetic operator is equivalent to x = x op (y) [...] In assignment operations, both the left- and right-hand expression lists must contain exactly one single-valued expression.

https://golang.org/ref/spec#Assignments