問題描述

我想專門化一個(gè)函數(shù)模板，以便返回類型根據(jù)模板參數(shù)的類型而變化.

I would like to specialize a function template such that the return type changes depending on the type of the template argument.

class ReturnTypeSpecialization
{
public:
    template<typename T>
    T Item();
};

// Normally just return the template type
template<typename T>
T ReturnTypeSpecialization::Item() { ... }

// When a float is specified, return an int
// This doesn't work:
template<float>
int ReturnTypeSpecialization::Item() { ... }

這可能嗎?我不能使用 C++11.

Is this possible? I can't use C++11.

推薦答案

由于專業(yè)化必須與返回類型的基本模板一致，您可以通過添加返回類型特征"來實(shí)現(xiàn)，您可以使用一個(gè)結(jié)構(gòu)專門化并從以下位置繪制真正的返回類型:

Since the specialization has to agree with the base template on the return type, you can make it so by adding a "return type trait", a struct you can specialize and draw the true return type from:

// in the normal case, just the identity
template<class T>
struct item_return{ typedef T type; };

template<class T>
typename item_return<T>::type item();

template<>
struct item_return<float>{ typedef int type; };
template<>
int item<float>();

現(xiàn)場示例.

請注意，您可能希望遵循以下規(guī)則，因此您只需更新 item_return 專業(yè)化中的 return-type.

Note that you might want to stick to the following, so you only need to update the return-type in the item_return specialization.

template<>
item_return<float>::type foo<float>(){ ... }
// note: No `typename` needed, because `float` is not a dependent type

這篇關(guān)于在函數(shù)模板特化中覆蓋返回類型的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網(wǎng)！