directory title
1. Conceptual distinction
In C++, templates are a way to achieve static polymorphism and a way to achieve generic programming.
First, let's understand the concepts of static polymorphism and generic programming:
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Static polymorphism : Static polymorphism is a way of achieving polymorphism at compile time. In C++, templates and function overloading are ways to achieve static polymorphism. The advantage of static polymorphism is that there is no runtime overhead, but the disadvantage is that all types and behaviors must be determined at compile time.
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Generic Programming : Generic programming is a programming paradigm where the goal is to write code that works on multiple types, rather than writing code for a single concrete type. In C++, templates are the main tool for implementing generic programming.
So, you can understand it this way: Templates are a language feature that can be used to implement static polymorphism and generic programming.
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When we use templates to write code that works on multiple types, we are doing generic programming. For example,
std::vector<T>is an example of generic programming, which can store elements of any type. -
When we use templates to choose different behaviors at compile time, we are using static polymorphism. For example, we can define a template function
template <typename T> void print(const T& t)and then provide specialized versions for different types, which is an example of static polymorphism.
In general, templates are a very powerful tool that allows us to customize types and behaviors at compile time, thereby improving code reusability and efficiency.
2 Templates for Static Polymorphism
In C++, templates are a powerful tool that can customize types and behaviors at compile time to achieve static polymorphism. Static polymorphism, also known as compile-time polymorphism, is a technique for determining the behavior of a function or object at compile time. The advantage of this technique is that there is no runtime overhead, but the disadvantage is that all types and behavior must be determined at compile time.
In this chapter, we will introduce how to use templates to achieve static polymorphism, including the use of function templates and class templates, as well as techniques for template specialization and partial specialization.
2.1 Function Templates and Class Templates
Function templates and class templates are the basis for implementing static polymorphism. By using templates, we can write a piece of code that can handle multiple types, and the compiler generates a special function or class for each type.
2.1.1 Function Templates¶
A function template is a special kind of function that can handle multiple types of arguments. For example, we can define a template function printthat prints any type of value:
template <typename T>
void print(const T& value) {
std::cout << value << std::endl;
}
We can call this function with any type of value, and the compiler will generate a special function for each type.
2.1.2 Class Templates
A class template is a special class that can handle multiple types of data. For example, we can define a template class Boxthat can store values of any type:
template <typename T>
class Box {
public:
Box(const T& value) : value_(value) {
}
const T& get() const {
return value_;
}
private:
T value_;
};
We can use any type of value to create an object of this class, and the compiler will generate a special class for each type.
2.2 Template Specialization and Partial Specialization
Template specialization and partial specialization are advanced techniques for implementing static polymorphism. By using specialization, we can provide special behavior for some specific types, and by using partial specialization, we can provide special behavior for a group of types.
2.3 Template Specialization
Template specialization allows us to provide special implementations for certain parameters of a template. This is a powerful tool that allows us to choose different behaviors based on types at compile time.
2.3.1 Function Template Specialization
For function templates, we can provide specializations for certain parameter types. printFor example, we could provide a specialization for the above function that prints std::vector<int>:
template <>
void print(const std::vector<int>& values) {
for (int value : values) {
std::cout << value << " ";
}
std::cout << std::endl;
}
This specialized version of the function will be called when the argument type std::vector<int>is .
2.3.2 Class Template Specialization
For class templates, we can also provide specializations for certain parameter types. BoxFor example, we could provide a specialized version of the above class that stores std::vector<int>:
template <>
class Box<std::vector<int>> {
public:
Box(const std::vector<int>& values) : values_(values) {
}
const std::vector<int>& get() const {
return values_;
}
size_t size() const {
return values_.size();
}
private:
std::vector<int> values_;
};
This specialized version of the class will be created when the parameter type std::vector<int>is .
2.4 Template Partial Specialization
Template partial specialization is a technique between full template and template specialization. It allows us to provide special implementations for a subset of template parameters. Template partial specialization only applies to class templates, not function templates.
BoxFor example, we could provide a partial specialization of the above class for storing any type of std::vector:
template <typename T>
class Box<std::vector<T>> {
public:
Box(const std::vector<T>& values) : values_(values) {
}
const std::vector<T>& get() const {
return values_;
}
size_t size() const {
return values_.size();
}
private:
std::vector<T> values_;
};
This partially specialized version of the class is created when the argument type is std::vector<T>(where it can be any type).T
Overall, template specialization and partial specialization are powerful tools for implementing static polymorphism. By using them, we can choose different behaviors according to the type at compile time, thus improving the flexibility and efficiency of the code.
3 Templates and Generic Programming
In C++, templates are a powerful tool that allow us to write code that can handle multiple types, rather than writing code for a single concrete type. This programming paradigm is known as generic programming. Generic programming can improve code reusability and maintainability, while also improving program performance.
3.1 Basic Concepts of Templates
In C++, templates can be used to define functions and classes. A template definition is like a blueprint that describes how to generate functions or classes for a specific set of types.
3.1.1 Function Templates¶
A function template is a special kind of function that can be used to process multiple types of data. The definition of a function template templatebegins with a keyword followed by a template parameter list, which contains one or more template parameters.
Here is an example of a function template:
template <typename T>
T max(T a, T b) {
return (a > b) ? a : b;
}
In this example, Tis a template parameter, which represents a type. maxWe can call functions with any type , such as max<int>(3, 4)or max<double>(3.14, 2.71).
3.1.2 Class Templates
A class template is a special class that can be used to generate many types of classes. The definition of a class template also templatebegins with the keyword followed by a list of template parameters.
Here is an example of a class template:
template <typename T>
class Stack {
public:
void push(const T& item) {
/*...*/ }
T pop() {
/*...*/ }
bool empty() const {
/*...*/ }
private:
std::vector<T> elements_;
};
In this example, Tis a template parameter, which represents a type. StackWe can create objects with any type , such as Stack<int>or Stack<std::string>.
3.2 Advanced Applications of Templates
Although the basic concept of templates is relatively simple, the application of templates in practice is very powerful. Through templates, we can implement complex generic algorithms, create efficient data structures, and even implement compile-time calculations.
3.2.1 Template Specialization
A template specialization is a special template that provides different implementations for some specific parameters of the template. We can define specializations for both function templates and class templates.
Template Specialization can be seen as both a form of static polymorphism and a part of generic programming.
First, template specialization can be seen as a form of static polymorphism, since it allows us to choose different implementations at compile time depending on the type. This is a kind of polymorphism, because we can use the same interface (i.e. template function or template class) to handle different types, and the specific behavior depends on the type. This kind of polymorphism is realized at compile time, so it is called static polymorphism.
Second, template specialization is also a part of generic programming because it is based on templates. The goal of generic programming is to write code that can handle multiple types, and template specialization is one way to achieve this goal. Through template specialization, we can provide specific implementations for certain parameters of the template, so that our code can better adapt to different types.
Therefore, template specialization can be seen as both a form of static polymorphism and a part of generic programming. These two concepts are not mutually exclusive, but complementary.
maxFor example, we could define a specialization of the function template above to handle std::stringarguments of type:
template <>
std::string max<std::string>(std::string a, std::string b) {
return (a.compare(b) > 0) ? a : b;
}
3.2.2 Template Metaprogramming
Template metaprogramming is a technique that uses templates for compile-time evaluation. Through template metaprogramming, we can perform some calculations before the program runs, thus improving the runtime performance of the program.
For example, we can use template metaprogramming to calculate the Fibonacci sequence:
template <int N>
struct Fibonacci {
static const int value = Fibonacci<N - 1>::value + Fibonacci<N - 2>::value;
};
template <>
struct Fibonacci<0> {
static const int value = 0;
};
template <>
struct Fibonacci<1> {
static const int value = 1;
};
In this example, Fibonacci<N>::valueit is calculated at compile time, so there is no overhead at runtime.
Templates are the main tool for implementing generic programming in C++, and they provide great flexibility and efficiency. Through a deep understanding and skilled use of templates, we can write more efficient and maintainable code.
epilogue
Comprehension is an important step towards the next level in our programming learning journey. However, mastering new skills and ideas always takes time and persistence. From a psychological point of view, learning is often accompanied by continuous trial and error and adjustment, which is like our brain gradually optimizing its "algorithm" for solving problems.
That's why when we encounter mistakes, we should see them as opportunities to learn and improve, not just obsessions. By understanding and solving these problems, we can not only fix the current code, but also improve our programming ability and prevent the same mistakes from being made in future projects.
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