• zwang <nehzgnaw gmail.com> Feb 01 2005
• Manfred Nowak <svv1999 hotmail.com> Feb 01 2005
• zwang <nehzgnaw gmail.com> Feb 01 2005

zwang <nehzgnaw gmail.com> writes:

The following C++ code correctly compiles and prints "C1":

   #include <cstdio>
   class C0{};
   class C1 : public C0{};
   class C2 : public C1{};
   class V{
   public:
     void v(C0& i){printf("C0");}
     void v(C1& i){printf("C1");}
   };
   int main(){
     V i;	
     C2 j;
     i.v(j);
     return 0;
   }

Here's the equivalent D version:

   class C0{}
   class C1 : C0{}
   class C2 : C1{}
   class V{
     void v(C0 i){printf("C0");}
     void v(C1 i){printf("C1");}
   }
   int main(){
     V i = new V;
     C2 j = new C2;
     i.v(j);
     return 0;
   }

... which does *not* compile.  DMD complains:
"function test.V.v overloads void(C0 i) and void(C1 i) both match 
argument list for v"

Why doesn't DMD implicitly cast C2 to C1 just like C++ compilers do?
Is this intended or a bug?

Manfred Nowak <svv1999 hotmail.com> writes:

zwang wrote:

[...]
 ... which does *not* compile.  DMD complains:
 "function test.V.v overloads void(C0 i) and void(C1 i) both match 
 argument list for v"
 
 Why doesn't DMD implicitly cast C2 to C1 just like C++ compilers
 do? Is this intended or a bug?


Congratulions for not reading the docs:
http://www.digitalmars.com/d/function.html#overloading

| In D, function overloading is simple. It matches exactly, it
| matches with implicit conversions, or it does not match. If there
| is more than one match, it is an error.

C2 can be implicitely casted to C1 and to C0. So there is more than one 
match and therefore an error.

-manfred 

zwang <nehzgnaw gmail.com> writes:

Thanks! I guess I'm still writing code in a c++ mindset.

Manfred Nowak wrote:
 Congratulions for not reading the docs:
 http://www.digitalmars.com/d/function.html#overloading
 
 | In D, function overloading is simple. It matches exactly, it
 | matches with implicit conversions, or it does not match. If there
 | is more than one match, it is an error.
 
 C2 can be implicitely casted to C1 and to C0. So there is more than one 
 match and therefore an error.
 
 -manfred