• terranium <spam here.lot> May 22 2008
• "Janice Caron" <caron800 googlemail.com> May 22 2008
• terranium <spam here.lot> May 22 2008
• "Janice Caron" <caron800 googlemail.com> May 22 2008
• "Koroskin Denis" <2korden gmail.com> May 22 2008

terranium <spam here.lot> writes:

Janice Caron Wrote:

 I like the following idea: if the case statement specifies a type,
 check that the object can be implicitly cast to that type; if the case
 statement specifies a value, check for equality. So:
 
     switch(typeof(a))
     {
         case B1: // RTTI dynamic cast test
             // ...
 
         case B2:
             // ...
     }
 

"Janice Caron" <caron800 googlemail.com> writes:

2008/5/22 terranium <spam here.lot>:
 there is no need for RTTI for *implicit* cast.


I know. So what?

terranium <spam here.lot> writes:

Janice Caron Wrote:

 2008/5/22 terranium <spam here.lot>:
 there is no need for RTTI for *implicit* cast.


 I know. So what?


so what's the meaning of

 check that the object can be implicitly cast to that type
 
     switch(typeof(a))
     {
         case B1: // RTTI dynamic cast test
     }

"Janice Caron" <caron800 googlemail.com> writes:

Well, convenience and readability, of course.

    switch(typeof(a))
    {
        case B1:
            // stuff
            break;

        case B2:
            // stuff
            break;

        case B3:
            // stuff
            break;
    }

looks cooler than

    {
        auto t = cast(B1)a;
        if (t != null)
        {
            // stuff
        }
    }
    {
        auto t = cast(B2)a;
        if (t != null)
        {
            // stuff
        }
    }
    {
        auto t = cast(B3)a;
        if (t != null)
        {
            // stuff
        }
    }

(in my opinion, at least). That said, I don't really care much about
this proposal one way or the other. It's only sugar, after all.

"Koroskin Denis" <2korden gmail.com> writes:

On Thu, 22 May 2008 17:30:14 +0400, Janice Caron <caron800 googlemail.com>  
wrote:

 Well, convenience and readability, of course.

     [skip]
    (in my opinion, at least). That said, I don't really care much about
 this proposal one way or the other. It's only sugar, after all.



terranium most probably found your fault with the following:

 check that the object can be implicitly cast to that type


Since implicit cast always succeeds, there is no need for such a switch,  
that's
why it should work with *explicit* cast only, it's an error otherwise:

class A {
}

class B : A {
}

class C {
}

B a = new B();
switch (b is) {
     case A: // always succeeds, and therefore makes no sense
         break;
     case C:
         doSomething();	// error, unreachable code
         break;
}