how can i use the derive-hierarchy at runtime for typechecking?

[Regan Heath]

dennis luehring wrote:
> Jarrett Billingsley schrieb:
>> "Chris Nicholson-Sauls" <ibisbasenji at gmail.com> wrote in message 
>> news:fcupko$kh7$2 at digitalmars.com...
>>
>>> void ifIs (S, T) (S obj, void delegate(T) dg) {
>>>   if (auto casted = cast(T) obj) dg(casted);
>>> }
>>
>> Or you could skip Downs' confusing way of writing code entirely ( ;) ) 
>> and just use:
>>
>> if(auto b = cast(B)foo)
>> {
>>     // do stuff with b
>> }
>>
> 
> and how can i insert this test in my base-class to hide the type stuff
> 
> class base
> {
>   int base_bla;
> 
>   bool is_derived_from( base other )
>   {
>     auto check = cast(typeof(this))other;
>     return !( check is null );
> 
>     // why can't i compile this

Because using 'auto' like this only works in an "if" statement. eg.

if ( auto check = cast(typeof(this))other ) return true;
return false;

>     // return ( auto check = cast(typeof(this))other );
>   }
> }
> 
> class test: base
> {
>   int test_bla;
> }
> 
> class blub: test
> {
>   int blub_bla;
> }
> 
> the is_derived_from test is always true
> maybe because of the base type parameter in is_derived_from

writefln(typeof(this).stringof) shows "base" even when called on an 
object of type "test" or "blub".  So, even if you say:

test t = new test;
blub b = new blub;

if (t.is_derived_from(b)) {} //is 'test' derived from 'blub'

you're really just asking if t is derived from "base", which it is (has 
to be to have the is_derived_from method - in this case)

Regan