C++ 11名decltype和數據成員

Question

下面的代碼編譯沒有任何錯誤：

class foo 
{ 
public: 
    void some_func() {} 
}; 

class bar 
{ 
private: 
    foo instance; 

public: 
    auto some_func() -> decltype(instance.some_func()) {} 
}; 

int main() {} 

雖然以下代碼中MSVC-12.0不編譯：

class foo 
{ 
public: 
    void some_func() {} 
}; 

class bar 
{ 
private: 
    foo instance; 

public: 
    auto some_func() -> decltype(instance.some_func()); 
}; 

auto bar::some_func() -> decltype(instance.some_func()) {} 

int main() {} 

這使我的以下錯誤：

error C2228: left of '.some_func' must have class/struct/union 
error C2556: 'int bar::some_func(void)' : overloaded function differs only by return type from 'void bar::some_func(void)' 
: see declaration of 'bar::some_func' 
error C2371: 'bar::some_func' : redefinition; different basic types 
: see declaration of 'bar::some_func' 

我在做什麼錯？我該如何解決它？

Answer 1

我現在沒有VS12，所以我有點猜測。在bar :: some_func的聲明中，當在類外聲明時，您無權訪問「實例」成員。

嘗試類似：

auto bar::some_func() -> decltype(bar::instance.some_func()) {}