声明和定义不匹配

Question

我的模板中的声明和定义不匹配class（所有不相关的内容都已删除）：

template <typename LanguageMap>
class WidgetLanguageManager
{
    public:
        enum class Language { DE, ENG, PL };
    protected:
        Language language;
        //Some protected fields
    public:
        explicit WidgetLanguageManager(const Language& language);
        explicit WidgetLanguageManager(const QString& language);
        Language ToLanguage(const QString& language);
    protected:
        //some protected methods
};


template <typename LanguageMap>
Language WidgetLanguageManager<LanguageMap>::ToLanguage(const QString& language) // this cannot be matched with a declaration
{
    for (QChar& c: language)
    {
        c = c.toLower();
    }

    switch (language)
    {
        case "german": return Language::DE;
        case "english": return Language::ENG;
        case "polish": return Language::PL;
    }
    throw RuntimeError("Wrong language paremeter.");
}

请帮忙，因为我看不出背后有任何原因。

Answer 1

以下方法可行：

template <typename LanguageMap>
typename WidgetLanguageManager<LanguageMap>::Language WidgetLanguageManager<LanguageMap>::ToLanguage(const QString& language)
// ^^^^^ 'typename' keyword needed because 'Language' is dependent name

由于 enum class Language 是 WidgetLanguageManager 模板 class 的一部分，您需要在它前面加上范围运算符。

Answer 2

除了额外的 typename，您可以使用尾随 return 类型：

template <typename LanguageMap>
auto WidgetLanguageManager<LanguageMap>::ToLanguage(const QString& language)
-> Language
{
/*..*/
}

声明和定义不匹配

Declaration and definition mismatch

c++

templates

declaration

definition

mismatch