[英]Ambiguous access to base class template member function
In Visual Studio 2008, the compiler cannot resolve the call to SetCustomer
in _tmain
below and make it unambiguous: 在Visual Studio 2008中,编译器无法解析对下面
_tmain
中的SetCustomer
的调用并使它明确:
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;
}
This is the compilation error: 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>'
I thought the template argument lookup mechanism would be smart enough to deduce the correct base Producer
. 我认为模板参数查找机制足够聪明,可以推断出正确的基本
Producer
。 Why isn't it? 为什么不呢
I could get around this by changing Producer
to 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_;
};
and call SetConsumer
as 并将
SetConsumer
称为
producer.SetConsumer<AppleConsumer>(&consumer); // Unambiguous call!!
but it would be nicer if I didn't have to... 但是如果我不必...那会更好
I thought the template argument lookup mechanism would be smart enough to deduce the correct base Producer.
我认为模板参数查找机制足够聪明,可以推断出正确的基本Producer。
This hasn't to do with templates, it comes from using multiple base classes - the name lookup is already ambiguous and overload resolution only takes place after that. 这与模板无关,它来自使用多个基类-名称查找已经模棱两可,并且仅在此之后才进行重载解析。
A simplified example would be the following: 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
Workarounds are explicitly qualifying the call or to introduce the functions into the derived classes scope: 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;
};
You can just use explicit qualification in your function call. 您可以在函数调用中使用显式限定。 Instead of:
代替:
producer.SetConsumer(&consumer);
try: 尝试:
producer.Producer<AppleConsumer>::SetConsumer(&consumer);
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