[英]C++ - Template Specialization & Partial Specialization
I have been looking all over the internet and stackoverflow for a concrete answer but I can't seem to find one. 我一直在寻找互联网和stackoverflow的具体答案,但我似乎无法找到一个。 I have to create a generic class and then implement specific functions.
我必须创建一个泛型类,然后实现特定的功能。 My specific instructions were: You need to make use of Template Expression Parameters and Template Class Specialization and Partial Specialization.
我的具体说明是:您需要使用模板表达式参数和模板类专业化和部分专业化。
I have a template class: 我有一个模板类:
template <class T, int x, int y>
class Z {
T **array[x][y];
public:
Z();
void print();
//and other methods
};
I need to: 我需要:
1) Only Z's where x= 2 and y = 2 need to have a public method void J() 1)只有Z的,其中x = 2和y = 2需要有一个公共方法void J()
2) For char Z's of x = 2 and y= 2 J will do something; 2)对于x = 2且y = 2 J的char Z,它会做某事; for everything else it does something else
对于其他一切,它做了别的事
3) For only Z's where T is char will the array be initialized to some value. 3)对于只有Z是char的字符,将数组初始化为某个值。 For everything else it's 0
其他一切都是0
Naturally, this works: 当然,这有效:
template<class T, int x, int y>
Z<T,x,y>::Z<T,x,y>() { //initialize to 0 }
But this doesn't: 但这不是:
template<int x, int y>
Z<char,x,y>::Z<char,x,y>() { //initialize to something}
And likewise (assume J exists) this does not work: 同样(假设J存在)这不起作用:
template <class T>
void Z<T,2,2>::J() { //something }
My question is: 我的问题是:
Is there any simple method for implementing the above items? 有没有简单的方法来实现上述项目? I need to keep all the other methods in Z. Giving a hint or pointing in the right direction (maybe I missed a question since there are a lot) would be helpful.
我需要在Z中保留所有其他方法。给出一个提示或指向正确的方向(也许我错过了一个问题,因为有很多)会有所帮助。
Thanks. 谢谢。
It seems you want to define only some functions of some specializations : if print()
does not change between the char
specialization and the general case, it seems that you don't want to redefine it. 您似乎只想定义某些特化的某些函数:如果
print()
在char
和一般情况之间没有变化,那么您似乎不想重新定义它。
// What you want to do (illegal in C++)
template<int,typename T>
struct Z
{
T myValue;
Z();
void print() { /* ... */ }
};
template<int i, typename T>
Z<i,T>::Z() { /* ... */ }
template<int i>
Z<i,char>::Z() { /* ... */ }
However, it does not work like this. 但是,它不会像这样工作。 Partial or full specializations of class have almost nothing in common, except 'prototype' of template parameters :
除了模板参数的“原型”之外,类的部分或完全特化几乎没有任何共同之处 :
// The two following types have only two things related: the template parameter is an int,
// and the second type is a full specialization of the first. There are no relations between
// the content of these 2 types.
template<int> struct A {};
template<> struct A<42> { void work(); };
You have to declare and define each (partial) specialization: 您必须声明并定义每个(部分)特化:
// Fixed example
template<int,typename T>
struct Z
{
T myValue;
Z();
void print() { /* ... */ }
};
template<int i, typename T>
Z<i,T>::Z() { /* ... */ }
// Specialization for <all-ints,char>
template<int i>
struct Z<i,char>
{
char myValue;
char othervalue;
Z();
void print() { /* Same code than for the general case */ }
};
template<int i>
Z<i,char>::Z() { /* ... */ }
The only way to escape the code duplication is by using inheritance of traits : 逃避代码重复的唯一方法是使用traits的继承:
// Example with the print function
template<typename T>
struct print_helper
{
void print() { /* ... */ }
};
// Fixed example
template<int,typename T>
struct Z : public print_helper<T>
{
T myValue;
Z();
};
template<int i, typename T>
Z<i,T>::Z() { /* ... */ }
// Specialization for <all-ints,char>
template<int i>
struct Z<i,char> : public print_helper<char>
{
char myValue;
char othervalue;
Z();
};
template<int i>
Z<i,char>::Z() { /* ... */ }
You cannot do what you want without duplication for the moment ( the feature removing code duplication is static if
and has been proposed for the next C++ standard, see n3322 and n3329 ). 目前你无法做到你想做的事情而没有重复(
static if
已经提出用于下一个C ++标准,删除代码重复的功能是static if
,请参阅n3322和n3329 )。
You may have a look at this course http://channel9.msdn.com/Series/C9-Lectures-Stephan-T-Lavavej-Core-C-/Stephan-T-Lavavej-Core-C-5-of-n 你可以看一下这门课程http://channel9.msdn.com/Series/C9-Lectures-Stephan-T-Lavavej-Core-C-/Stephan-T-Lavavej-Core-C-5-of-n
While this is not possible that you define partial specialization for function templates, you can define partial specialization for class or struct template. 虽然您无法为函数模板定义部分特化,但您可以为类或结构模板定义部分特化。
template<typename T> struct helper {
static void doThingy(){}
};
template<typename X> struct helper<X*> {
static void doThingy(){}
};
Helper(double*)::doThingy();
In this example, you want to specialize behavior in doThingy() only when the type in template is a pointer type. 在此示例中,仅当模板中的类型是指针类型时,才希望在doThingy()中特化行为。 You cannot use overload of method doThingy() in this case.
在这种情况下,您不能使用方法doThingy()的重载。 This is because you cannot overload a function with no arguments.
这是因为您不能重载没有参数的函数。 But you can have partial specialization of the struct helper.
但是你可以对struct helper进行部分特化。 In specialized template, you implemented wished behavior for the doThingy().
在专用模板中,您实现了doThingy()的所需行为。
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