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Abstract Method

Guys I wanted to create an abstract method; however, compiler gives me error. Is it not possible to create one or there is another way rather than the pure c++ coding(e.g. UFUNCTION(bla bla))?

Abstract Class:

 UCLASS(abstract)
 class THECLOUDGAME_API AGround : public AMovingPawn
 {
     GENERATED_UCLASS_BODY()
     
 protected:
     virtual TArray<AGround*> GetFollowingGrounds(void) = 0;
 };
 


Error:

 1>C:\Users\ErayT\UnrealEngine\UnrealEngine_4.3\Engine\Source\Runtime\CoreUObject\Public\UObject\Class.h(2151): error C2259: 'AGround' : cannot instantiate abstract class
 1>          due to following members:
 1>          'TArray<AGround *,FDefaultAllocator> AGround::GetFollowingGrounds(void)' : is abstract
 1>          C:\Users\ErayT\Documents\Unreal Projects\TheCloudGame\Source\TheCloudGame\Elements/Grounds/Ground.h(23) : see declaration of 'AGround::GetFollowingGrounds'
 1>          C:\Users\ErayT\UnrealEngine\UnrealEngine_4.3\Engine\Source\Runtime\CoreUObject\Public\UObject\Class.h(2189) : see reference to function template instantiation 'void InternalConstructor<TClass>(const FPostConstructInitializeProperties &)' being compiled
 1>          with
 1>          [
 1>              TClass=AGround
 1>          ]
 1>          C:\Users\ErayT\Documents\Unreal Projects\TheCloudGame\Intermediate\Build\Win64\Inc\TheCloudGame\TheCloudGame.generated.cpp(30) : see reference to function template instantiation 'void GetPrivateStaticClassBody<AGround>(const TCHAR *,const TCHAR *,UClass *&,void (__cdecl *)(void))' being compiled
 1> 

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asked Aug 20 '14 at 07:08 PM in C++ Programming

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ErayT
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2 answers: sort voted first

You can't use the C++ syntax for this because the Class Default Object gets instantiated. We usually use:

 virtual void MyFunc() { check(0 && "You must override this"); }

Compile time would be better but this works too

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answered Aug 20 '14 at 09:22 PM

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joeGraf STAFF
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avatar image ErayT Aug 21 '14 at 12:23 PM

Can you help me about the returning value?

In my example a TArray must be returned. Is there a trick not to return or how can I return a null value?

avatar image joeGraf STAFF Aug 21 '14 at 02:37 PM

Sorry, I missed that.

 virtual TArray<AGround*> MyFunc() { check(0 && "You must override this"); return TArray<AGround *>(); }
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Another way:

 virtual TArray<int32> MyFunc()
 {
     unimplemented();
     return TArray<int32>();
 }

But no compile time support too.

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answered Apr 09 '18 at 07:31 AM

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Krustenkaese
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