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February 08, 2012
Checking runtime object type
What's the correct syntax for checking the runtime type of a derived
object given its base class pointer? I tried:

	Base f() { return new Derived(); }
	Base b = f();
	assert(is(typeof(b)==Derived));

but it throws an error. Apparently typeof(b)==Base; so typeof returns
only compile-time information? How do I get at the runtime type?


T

-- 
"You are a very disagreeable person." "NO."
February 08, 2012
Re: Checking runtime object type
Am Wed, 8 Feb 2012 11:20:39 -0800
schrieb "H. S. Teoh" <hsteoh@quickfur.ath.cx>:

> What's the correct syntax for checking the runtime type of a derived
> object given its base class pointer? I tried:
> 
> 	Base f() { return new Derived(); }
> 	Base b = f();
> 	assert(is(typeof(b)==Derived));
> 
> but it throws an error. Apparently typeof(b)==Base; so typeof returns
> only compile-time information? How do I get at the runtime type?
> 
> 
> T
> 

I think using casts is the only way:

Base f() { return new Derived(); }
Base b = f();
auto c = cast(Derived)b;
assert(c !is null);
February 08, 2012
Re: Checking runtime object type
On Wed, 08 Feb 2012 11:20:39 -0800, H. S. Teoh wrote:

> What's the correct syntax for checking the runtime type of a derived
> object given its base class pointer? I tried:
> 
> 	Base f() { return new Derived(); }
> 	Base b = f();
> 	assert(is(typeof(b)==Derived));
> 
> but it throws an error. Apparently typeof(b)==Base; so typeof returns
> only compile-time information? How do I get at the runtime type?
> 
> 
> T

Yeah, is() and typeof() are purely compile-time. You'll want the typeid 
expression (http://d-programming-language.org/
expression.html#typeidexpression) which returns an instance of TypeInfo 
(http://d-programming-language.org/phobos/object.html#TypeInfo).
February 08, 2012
Re: Checking runtime object type
On Wednesday, February 08, 2012 20:21:45 Johannes Pfau wrote:
> Am Wed, 8 Feb 2012 11:20:39 -0800
> 
> schrieb "H. S. Teoh" <hsteoh@quickfur.ath.cx>:
> > What's the correct syntax for checking the runtime type of a derived
> > 
> > object given its base class pointer? I tried:
> > Base f() { return new Derived(); }
> > Base b = f();
> > assert(is(typeof(b)==Derived));
> > 
> > but it throws an error. Apparently typeof(b)==Base; so typeof returns
> > only compile-time information? How do I get at the runtime type?
> > 
> > 
> > T
> 
> I think using casts is the only way:
> 
> Base f() { return new Derived(); }
> Base b = f();
> auto c = cast(Derived)b;
> assert(c !is null);

Casting is definitely the way that you're supposed to do it. If the cast 
results in null, then the class is _not_ of the type that you cast to. e.g.

if(auto d = cast(Derived) b)
//do stuff with d

- Jonathan M Davis
February 08, 2012
Re: Checking runtime object type
On Wed, 08 Feb 2012 14:41:51 -0500, Jonathan M Davis <jmdavisProg@gmx.com>  
wrote:

> On Wednesday, February 08, 2012 20:21:45 Johannes Pfau wrote:
>> Am Wed, 8 Feb 2012 11:20:39 -0800
>>
>> schrieb "H. S. Teoh" <hsteoh@quickfur.ath.cx>:
>> > What's the correct syntax for checking the runtime type of a derived
>> >
>> > object given its base class pointer? I tried:
>> > Base f() { return new Derived(); }
>> > Base b = f();
>> > assert(is(typeof(b)==Derived));
>> >
>> > but it throws an error. Apparently typeof(b)==Base; so typeof returns
>> > only compile-time information? How do I get at the runtime type?
>> >
>> >
>> > T
>>
>> I think using casts is the only way:
>>
>> Base f() { return new Derived(); }
>> Base b = f();
>> auto c = cast(Derived)b;
>> assert(c !is null);
>
> Casting is definitely the way that you're supposed to do it. If the cast
> results in null, then the class is _not_ of the type that you cast to.  
> e.g.
>
> if(auto d = cast(Derived) b)
>  //do stuff with d

It depends on the usage.  If you want to see what the most derived type  
is, using typeid is best (for those old-schoolers, this used to be  
.classinfo).

If you want to *verify* that the given type is derived from some other  
type, using cast is best.

-Steve
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