“multiple overloads” using templated class with duplicate types

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I'm trying to write a class that takes two templated types. This class inherits from an interface. See the below code.



#include <iostream>
#include <string>

template <typename T>
class IObserver 
 public:
 virtual void Next(const T& value) noexcept = 0;
;

template <typename T1, typename T2>
class BinaryObserver : public IObserver<T1>, public IObserver<T2> 
 public:
 void Next(const T1& value) noexcept override;

 void Next(const T2& value) noexcept override;
;

int main() 
 // This is OK
 BinaryObserver<int, float> mc1;
 mc1.Next(0);
 mc1.Next(0.0f);

 // This fails to compile with "multiple overloads"
 BinaryObserver<int, int> mc2;
 mc2.Next(0);
 mc2.Next(0);



I'm having trouble when T1 is the same type as T2. Obviously this means two Next functions will be generated with the same type, which gives an error: multiple overloads of 'Next' instantiate to the same signature.



What's an idiomatic way of fixing this? I'm not sure how to handle the case when T1=T2 since I'd only need one Next function generated



Thanks!






c++ c++11 templates overloading







share|improve this question























  • It's not just the multiple overloads (which you can fix with some enable_if magic) but you are also deriving twice from the same base class which is also not allowed. @VTT's answer fixes both issues.
    – Alan Birtles
    1 hour ago














up vote
7
down vote

favorite
1












I'm trying to write a class that takes two templated types. This class inherits from an interface. See the below code.



#include <iostream>
#include <string>

template <typename T>
class IObserver 
 public:
 virtual void Next(const T& value) noexcept = 0;
;

template <typename T1, typename T2>
class BinaryObserver : public IObserver<T1>, public IObserver<T2> 
 public:
 void Next(const T1& value) noexcept override;

 void Next(const T2& value) noexcept override;
;

int main() 
 // This is OK
 BinaryObserver<int, float> mc1;
 mc1.Next(0);
 mc1.Next(0.0f);

 // This fails to compile with "multiple overloads"
 BinaryObserver<int, int> mc2;
 mc2.Next(0);
 mc2.Next(0);



I'm having trouble when T1 is the same type as T2. Obviously this means two Next functions will be generated with the same type, which gives an error: multiple overloads of 'Next' instantiate to the same signature.



What's an idiomatic way of fixing this? I'm not sure how to handle the case when T1=T2 since I'd only need one Next function generated



Thanks!






c++ c++11 templates overloading







share|improve this question























  • It's not just the multiple overloads (which you can fix with some enable_if magic) but you are also deriving twice from the same base class which is also not allowed. @VTT's answer fixes both issues.
    – Alan Birtles
    1 hour ago












up vote
7
down vote

favorite
1









up vote
7
down vote

favorite
1






1





I'm trying to write a class that takes two templated types. This class inherits from an interface. See the below code.



#include <iostream>
#include <string>

template <typename T>
class IObserver 
 public:
 virtual void Next(const T& value) noexcept = 0;
;

template <typename T1, typename T2>
class BinaryObserver : public IObserver<T1>, public IObserver<T2> 
 public:
 void Next(const T1& value) noexcept override;

 void Next(const T2& value) noexcept override;
;

int main() 
 // This is OK
 BinaryObserver<int, float> mc1;
 mc1.Next(0);
 mc1.Next(0.0f);

 // This fails to compile with "multiple overloads"
 BinaryObserver<int, int> mc2;
 mc2.Next(0);
 mc2.Next(0);



I'm having trouble when T1 is the same type as T2. Obviously this means two Next functions will be generated with the same type, which gives an error: multiple overloads of 'Next' instantiate to the same signature.



What's an idiomatic way of fixing this? I'm not sure how to handle the case when T1=T2 since I'd only need one Next function generated



Thanks!






c++ c++11 templates overloading







share|improve this question















I'm trying to write a class that takes two templated types. This class inherits from an interface. See the below code.



#include <iostream>
#include <string>

template <typename T>
class IObserver 
 public:
 virtual void Next(const T& value) noexcept = 0;
;

template <typename T1, typename T2>
class BinaryObserver : public IObserver<T1>, public IObserver<T2> 
 public:
 void Next(const T1& value) noexcept override;

 void Next(const T2& value) noexcept override;
;

int main() 
 // This is OK
 BinaryObserver<int, float> mc1;
 mc1.Next(0);
 mc1.Next(0.0f);

 // This fails to compile with "multiple overloads"
 BinaryObserver<int, int> mc2;
 mc2.Next(0);
 mc2.Next(0);



I'm having trouble when T1 is the same type as T2. Obviously this means two Next functions will be generated with the same type, which gives an error: multiple overloads of 'Next' instantiate to the same signature.



What's an idiomatic way of fixing this? I'm not sure how to handle the case when T1=T2 since I'd only need one Next function generated



Thanks!






c++ c++11 templates overloading




c++ c++11 templates overloading






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edited 2 hours ago

























asked 2 hours ago









Sam P

1,411824




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  • It's not just the multiple overloads (which you can fix with some enable_if magic) but you are also deriving twice from the same base class which is also not allowed. @VTT's answer fixes both issues.
    – Alan Birtles
    1 hour ago
















  • It's not just the multiple overloads (which you can fix with some enable_if magic) but you are also deriving twice from the same base class which is also not allowed. @VTT's answer fixes both issues.
    – Alan Birtles
    1 hour ago















It's not just the multiple overloads (which you can fix with some enable_if magic) but you are also deriving twice from the same base class which is also not allowed. @VTT's answer fixes both issues.
– Alan Birtles
1 hour ago




It's not just the multiple overloads (which you can fix with some enable_if magic) but you are also deriving twice from the same base class which is also not allowed. @VTT's answer fixes both issues.
– Alan Birtles
1 hour ago












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How about a specialization:



template <typename T>
class BinaryObserver<T, T> : public IObserver<T> 
 public:
 void Next(const T & value) noexcept override;
;





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    up vote
    9
    down vote













    How about a specialization:



    template <typename T>
    class BinaryObserver<T, T> : public IObserver<T> 
     public:
     void Next(const T & value) noexcept override;
    ;





    share|improve this answer
























      up vote
      9
      down vote













      How about a specialization:



      template <typename T>
      class BinaryObserver<T, T> : public IObserver<T> 
       public:
       void Next(const T & value) noexcept override;
      ;





      share|improve this answer






















        up vote
        9
        down vote










        up vote
        9
        down vote









        How about a specialization:



        template <typename T>
        class BinaryObserver<T, T> : public IObserver<T> 
         public:
         void Next(const T & value) noexcept override;
        ;





        share|improve this answer












        How about a specialization:



        template <typename T>
        class BinaryObserver<T, T> : public IObserver<T> 
         public:
         void Next(const T & value) noexcept override;
        ;






        share|improve this answer












        share|improve this answer



        share|improve this answer










        answered 2 hours ago









        VTT

        21.5k32143




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