简而言之:
有什么方法可以喂养General
模板化类仅代表一个enum
类型?就像是:
template <typename T> struct General {};
struct EnumSpecific : General<any_enum_type> {};
<int>
太多/在我的情况下不起作用。
我的具体案例:
- 一个模板化的
Holder
类以通用方式处理任何类型的数据。
- 摘要
General
类实现特定的算法依赖于Holder
的行为。
- 模板规格
General
(like IntSpecific
, DoubleSpecific
, StringSpecific
, MoreSophisticatedTypeSpecific
..) 定义如何处理一些具体的Holder
types.
- 我怎样才能正确定义
EnumSpecific
规格?
这是导致我的问题发生的简化代码:
// A templated value holder:
template <typename T>
class Holder {
public:
Holder(T const& t) : _value(t) {};
// generic methods
void generics() {};
// methods concerning the value:
void set(T const& t /*, setInfo */) {
// .. check for an actual change, notify buddies of the change..
_value = t;
};
T value(/*readInfo*/) {
// .. do stuff depending on how / why the value is read..
return _value;
};
private:
T _value;
};
// (in reality, all `generics` methods come from a parent, untemplated class)
// A generic process involving such `Holder`s:
template <typename T>
class General {
public:
typedef bool /* or anything */ KnownReturnTypes;
General(Holder<T>* const a
, Holder<T>* const b)
: _a(a)
, _b(b)
{};
void methods() {
// Use common behavior of all `Holder`'s
_a->generics();
// .. or methods that rely on the actual values:
KnownReturnTypes knr( valuedMethods() );
if (knr) {} else {}
// ...
};
// Use polymorphism to adapt to each situation..
virtual KnownReturnTypes valuedMethods() = 0;
protected:
Holder<T>* _a;
Holder<T>* _b;
};
// Example of specialization for integral types (there might be others)
class IntSpecific : General<int> {
public:
IntSpecific(Holder<int>* const a
, Holder<int>* const b)
: General<int>(a, b)
{};
// implement the valuedMethods:
virtual KnownReturnTypes valuedMethods() {
return _a->value() > _b->value(); // dummy
}
};
// Specialization for enum types:
// * * * class EnumSpecific : General<any_enum_type> { // does not exist * *
class EnumSpecific : General<int> {
public:
EnumSpecific( Holder<int>* const a
, Holder<int>* const b)
: General<int>(a, b)
{};
// only use properties and methods offered by an enum type:
virtual KnownReturnTypes valuedMethods() {
return _a->value() == _b->value(); // dummy
}
};
// One particular case
typedef enum {One, Two, Three} Enum;
typedef Holder<Enum> EnumHolder;
int main() {
// Check that `IntSpecific` works fine.
Holder<int>* i( new Holder<int>(3) );
Holder<int>* j( new Holder<int>(5) );
IntSpecific is(i, j); // ok.
// Try the `EnumSpecific`
EnumHolder* a( new EnumHolder { One } );
EnumHolder* b( new EnumHolder { Two } );
EnumSpecific es(static_cast<Holder<int>*>(a) // invalid cast
, static_cast<Holder<Enum>*>(b)); // unexpected type
// This is because the compiler doesn't know enough about what
// EnumSpecific actually *is*. How to tell him more about it?
return EXIT_SUCCESS;
}
我应该在模板参数中添加什么EnumSpecific : General<??>
让编译器清楚地了解事情?
我需要使用某种enum_type
通用编程的概念和更复杂的工具?