Submission: switch (...) instanceof feature

[Gabriel Belingueres]

touché!

Maybe it is time to consider an idiom like C++'s dynamic_cast?

void f() {
  Object x = foo();
  String s = dynamic_cast<String>(x);
  if (s != null) {
    m(s); // call m(String)
    m(x); // call m(Object);
  }
}

2009/5/4 Rémi Forax <forax at univ-mlv.fr>:
> Reinier Zwitserloot a écrit :
>> Why is this neccessary? We have a similar situation here as the
>> inherited exception issue: Rare and definitely broken (at runtime)
>> code will now break at compile time. This is technically 'backwards
>> incompatible', insofar that code that used to compile no longer does.
>> However, I believe the decision was made that this technical
>> incompatibility was acceptable, because the code made no runtime sense
>> in the first place. You have the same situation here:
>>
>>
>> old code:
>>
>> Object x = foo();
>>
>> if ( x instanceof String ) {
>>    Integer y = (Integer)x;
>> }
>>
>> would compile, eventhough it's clearly bogus. With this change:
>>
>> if ( x instanceof String ) {
>>     //within this block, 'x' is considered to be both a String and
>> whatever x's actual type is, if it's not a strict supertype of String.
>> }
>>
>
> This change is not backward compatible ...
>
> class A {
>  void m(String) { ... }
>  void m(Object o) { ... }
>
>  void f() {
>    Object x = foo();
>    if ( x instanceof String ) {
>      m(x);      <--  call m(Object), will call m(String)
>   }
>  }
> }
>
> [ ... ]
>
>>   --Reinier Zwitserloot
>> Like it? Tip it!
>> http://tipit.to
>>
>
> Rémi
>
>