code: def get_instance_assignment(self, ctx):
          
          if ctx is None:
              return None
  
          visitor = ExprVisitor(self.compiler)
          expr = visitor.visit(ctx.expr())
          expr = expressions.AssignmentCast(self.compiler.env, SourceRef.from_antlr(ctx.op), expr, int)
          expr.predict_type()
          return expr
docs: Gets the integer expression in any of the four instance assignment
          operators ('=' '@' '+=' '%=')