Where is += method located for int in scala

Question

Is +=(or any assignment operators) a method in scala for Int type.

For example,

var x=5 x+=1

Here I am able to use += method only when it is a variable.

I am not able to do,

5+=1

Does scala compiler considers this method as a special case?

Why it is not available in scala.Int class?

What do you expect 5+=1 to actually do? I don't know Scala, but I don't see any reason for it to allow you to overwrite a primitive's value... — CptBartender
– CptBartender, Commented Apr 29, 2016 at 12:05
I thought there is no operator in scala(only methods), so there will not be a difference between value and variable. — Hariharan
– Hariharan, Commented Apr 29, 2016 at 12:09
5.+(1) and x.+(1) will work consistently, so I expect this operator to behave in the same way. — Hariharan
– Hariharan, Commented Apr 29, 2016 at 12:11

Lee · Accepted Answer · 2016-04-29 12:10:40Z

There is no += method, it is expanded to x = x + 1 by the compiler. This is detailed in the specification:

6.12.4 Assignment Operators

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.

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 +=.

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 +.

So you could do this for any method that fulfills the condition? E.g. obj1 concat= obj2?
@LukaJacobowitz - I don't think so, this only applies to operators which are lexically non-empty sequences of operator characters. The lexical syntax section defines operator chars as printable ascii characters which are not whitespace, letters, digits, parenthesis or delimiters.

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