• H. S. Teoh (10/10) Feb 08 2012 What's the correct syntax for checking the runtime type of a derived
• Johannes Pfau (7/20) Feb 08 2012 I think using casts is the only way:
• Jonathan M Davis (6/28) Feb 08 2012 Casting is definitely the way that you're supposed to do it. If the cast...
• Steven Schveighoffer (8/36) Feb 08 2012 It depends on the usage. If you want to see what the most derived type ...
• Justin Whear (5/17) Feb 08 2012 Yeah, is() and typeof() are purely compile-time. You'll want the typeid

"H. S. Teoh" <hsteoh quickfur.ath.cx> writes:

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."

Johannes Pfau <nospam example.com> writes:

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);

"Jonathan M Davis" <jmdavisProg gmx.com> writes:

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

"Steven Schveighoffer" <schveiguy yahoo.com> writes:

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

Justin Whear <justin economicmodeling.com> writes:

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).