在Visual Studio 2008中,编译器无法解析对下面的SetCustomer中的_tmain的调用,并且使它明确:

template <typename TConsumer>
struct Producer
{
    void SetConsumer(TConsumer* consumer) { consumer_ = consumer; }

    TConsumer* consumer_;
};

struct AppleConsumer
{
};

struct MeatConsumer
{
};

struct ShillyShallyProducer : public Producer<AppleConsumer>,
                              public Producer<MeatConsumer>
{
};

int _tmain(int argc, _TCHAR* argv[])
{
    ShillyShallyProducer producer;
    AppleConsumer consumer;
    producer.SetConsumer(&consumer);   //  <--- Ambiguous call!!

    return 0;
}

这是编译错误:
// error C2385: ambiguous access of 'SetConsumer'
//    could be the 'SetConsumer' in base 'Producer<AppleConsumer>'
//    or could be the 'SetConsumer' in base 'Producer<MeatConsumer>'

我认为模板参数查找机制足够聪明,可以推断出正确的基础Producer。为什么不呢

我可以通过将Producer更改为
template <typename TConsumer>
struct Producer
{
    template <typename TConsumer2>
    void SetConsumer(TConsumer2* consumer) { consumer_ = consumer; }

    TConsumer* consumer_;
};

并调用SetConsumer
    producer.SetConsumer<AppleConsumer>(&consumer);   // Unambiguous call!!

但是如果我不必...那会更好

最佳答案



这与模板无关,它来自使用多个基类-名称查找已经是模棱两可的,并且仅在此之后才进行重载解析。

一个简化的示例如下:

struct A { void f()    {} };
struct B { void f(int) {} };
struct C : A, B {};

C c;
c.f(1); // ambiguous

解决方法是显式限定调用资格或将函数引入派生类范围:
 struct ShillyShallyProducer : public Producer<AppleConsumer>,
                               public Producer<MeatConsumer>
 {
     using Producer<AppleConsumer>::SetConsumer;
     using Producer<MeatConsumer >::SetConsumer;
 };

09-10 04:16
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