Question

I am attempting to add an update method to the Symbol class.

class SymbolUpdate(s: Symbol) {
    def update(i: Int) = s.name + i
}
implicit def toSymbolUpdate(s: Symbol) = new SymbolUpdate(s)

But when I run the code I get the following

scala> 's = 1
<console>:327: error: value update is not a member of object Symbol
              's = 1
              ^

But it does work when I call the method directly.

scala> 's.update(1)
res41: java.lang.String = s1

Or if I explicitly put an empty argument array.

scala> 's() = 1
res42: java.lang.String = s1

Not sure what the problem is with my code?

Answer 1

According to the Scala Language Spec:

An assignment f(args) = e with a function application to the left of the ‘=’ operator is interpreted as f.update(args, e), i.e. the invocation of an update function
defined by f.

It’s especially clear if you read the corresponding section in Programming in Scala:

Similarly, when an assignment is made to a variable to which parenthesis and one or more arguments have been applied, the compiler will transform that into an invocation of an update methods that takes the arguments in parenthesis as well as the object to the right of the equals sign.

Together, I take it to mean that the parenthesis are required.