[英]Inheriting both abstract base interface and its implementation gives C2259
I have the following condition:我有以下条件:
An absract base class with many pure virtual functions:具有许多纯虚函数的抽象基类:
interface IBase
{
virtual void foo1() = 0;
virtual void foo2() = 0;
virtual void foo3() = 0;
virtual void foo4() = 0;
virtual void foo5() = 0;
// ...
virtual void fooN() = 0;
};
Two small interfaces that inherit it:继承它的两个小接口:
Version-A:版本-A:
interface IBaseExt_A :
public IBase
{
virtual void foo_A() = 0;
};
Version-B:版本-B:
interface IBaseExt_B :
public IBase
{
virtual void foo_B() = 0;
};
I create base class that implements all of the IBase
interface functions:我创建了实现所有IBase
接口函数的基类:
class CBase :
public IBase
{
public:
virtual void foo1() { /* Do something... */}
virtual void foo2() { /* Do something... */}
virtual void foo3() { /* Do something... */}
virtual void foo4() { /* Do something... */}
virtual void foo5() { /* Do something... */}
// ...
virtual void fooN() { /* Do something... */}
};
Now, I want to implement both derived versions with minimal code .现在,我想用最少的代码实现两个派生版本。
I was hoping to do something like:我希望做这样的事情:
class CBaseExt_A :
public IBaseExt_A,
public CBase
{
public:
virtual void foo_A() { /* Do something... */}
};
Apparently this gives error:显然这给出了错误:
C2259: 'CBaseExt_A': cannot instantiate abstract class...
These errors refer to all IBase
interface functions.这些错误涉及所有IBase
接口函数。
I know I can solve it the long way by delegating all IBase
functions to CBase
implementation:我知道我可以通过将所有IBase
函数委托给CBase
实现来解决这个问题:
class CBaseExt_A :
public IBaseExt_A,
public CBase
{
// IBase implementation:
public:
virtual void foo1() { CBase::foo1();}
virtual void foo2() { CBase::foo2();}
virtual void foo3() { CBase::foo3();}
virtual void foo4() { CBase::foo4();}
virtual void foo5() { CBase::foo5();}
// ...
virtual void fooN() { CBase::fooN();}
// IBaseExt_A implementation:
public:
virtual void foo_A() { /* At last - do what we came here for...*}
};
But this makes my small class CBaseExt_A
become big and complex.但这使得我的小类CBaseExt_A
变得庞大而复杂。
Is there a way how to avoid all this manual delegation coding?有没有办法避免所有这些手动委托编码?
Many thanks, PazO非常感谢,帕兹奥
You should use the following code:您应该使用以下代码:
interface IBase
{
virtual void foo() = 0;
......
};
class CBase : virtual public IBase
{
void foo() { }
......
};
interface IBaseExt_A : virtual public IBase
{
virtual void foo_A() = 0;
};
struct CBaseExt_A : public IBaseExt_A, public CBase
{
virtual void foo_A() { /* Do something... */ }
};
Note that both places where the IBase
class is inherited should be marked as virtual.请注意,继承IBase
类的两个地方都应标记为虚拟。
I think you should specify one of the two inheritance to be virtual.我认为你应该指定两个继承之一是虚拟的。
That is a diamond inheritance where那是钻石的传承
IBase is the top level IBase 是顶级的
IBaseExt_A and CBase are the middle level IBaseExt_A 和 CBase 是中间层
CBaseExt_A is the bottom level CBaseExt_A 是底层
so in CBaseExt_A you want to specify from which path implement the top level, I would say that you may want to specify CBase inheritance in IBaseExt_A to be public virtual instead of just public.所以在 CBaseExt_A 中你想指定从哪个路径实现顶级,我想说你可能想在 IBaseExt_A 中指定 CBase 继承是公共虚拟而不是公共虚拟。
class CBaseExt_A :
public IBaseExt_A,
public virtual CBase
{
public:
virtual void foo_A() { /* Do something... */}
};
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