[cpplings] Add template programming exercises (#526)

### What problem were solved in this pull request?

Issue Number:  #523

Problem:
- Missing C++ template programming exercises, affecting contributors'
understanding and application of C++ templates
- Need to enhance the cpplings exercise collection to support the goal
of Issue #508

### What is changed and how it works?

- Added template_basics.cpp file, implementing:
- Basic function template examples showing how to create generic
functions
- Class template implementation and usage, demonstrating definition and
usage of generic classes
- Template specialization techniques with a specialized version for
string type
- Recursive implementation of variadic templates, showing how to handle
variable parameter lists
- SFINAE technique application, selecting different function
implementations based on type traits

- Added comprehensive comments explaining template programming concepts
and use cases
- Included complete test code to ensure examples run correctly

### Other information
- Run the test case with `./bin/cpplings template_basics`
- Parent Issue: #508 (add more cpplings case)

Author: XueSongTap

src/cpplings/CMakeLists.txt

@@ -13,3 +13,4 @@ add_custom_executable(lambda lambda.cpp)
 add_custom_executable(lock lock.cpp)
 add_custom_executable(mutex mutex.cpp)
 add_custom_executable(smart_pointer smart_pointer.cpp)
+add_custom_executable(template template.cpp)

src/cpplings/template.cpp

@@ -0,0 +1,139 @@
+/* Copyright (c) 2021 OceanBase and/or its affiliates. All rights reserved.
+miniob is licensed under Mulan PSL v2.
+You can use this software according to the terms and conditions of the Mulan PSL v2.
+You may obtain a copy of Mulan PSL v2 at:
+         http://license.coscl.org.cn/MulanPSL2
+THIS SOFTWARE IS PROVIDED ON AN "AS IS" BASIS, WITHOUT WARRANTIES OF ANY KIND,
+EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO NON-INFRINGEMENT,
+MERCHANTABILITY OR FIT FOR A PARTICULAR PURPOSE.
+See the Mulan PSL v2 for more details. */
+
+// 模板编程是C++中的一种强大特性，允许开发者编写与类型无关的代码。
+// 模板可以应用于函数、类和变量，使开发者能够编写通用的算法和数据结构。
+//
+// C++模板主要分为函数模板和类模板两种：
+// 函数模板允许创建可以处理多种数据类型的函数，而不必为每种类型编写单独的函数。
+// 类模板允许创建可以存储和处理多种数据类型的通用类，例如STL中的容器。
+// 模板特化允许为特定的类型提供专门的实现。
+// 变参模板支持接受可变数量的参数，非常适用于构建递归数据结构和算法。
+// SFINAE（Substitution Failure Is Not An Error）是一种模板编程技术，它允许在编译时根据类型特性选择正确的
+// 函数重载或模板特化。当模板参数替换失败时，不会产生编译错误，而是简单地从重载解析
+// 集合中删除该函数。
+#include <iostream>
+#include <type_traits>
+#include <vector>
+#include <string>
+
+// 1. 基础函数模板
+template <typename T>
+T max_value(T a, T b)
+{
+  return (a > b) ? a : b;
+}
+
+// 2. 类模板
+template <typename T>
+class Container
+{
+private:
+  T data;
+
+public:
+  Container(T value) : data(value) {}
+
+  T get_data() const { return data; }
+
+  void set_data(T value) { data = value; }
+};
+
+// 3. 模板特化 - 为std::string类型提供特殊实现
+template <>
+class Container<std::string>
+{
+private:
+  std::string data;
+
+public:
+  Container(std::string value) : data(value) {}
+
+  std::string get_data() const { return data; }
+
+  void set_data(std::string value) { data = value; }
+
+  // 字符串类型特有的方法
+  std::size_t length() const { return data.length(); }
+};
+
+// 4. 变参模板 - 递归终止条件
+template <typename T>
+T sum(T value)
+{
+  return value;
+}
+
+// 变参模板 - 递归调用
+template <typename T, typename... Args>
+T sum(T first, Args... args)
+{
+  return first + sum(args...);
+}
+
+// 5. SFINAE技术示例
+// SFINAE (Substitution Failure Is Not An Error) 是C++模板编程中的重要概念：
+// - 它允许编译器在模板替换过程中，当某个替换导致无效代码时，不产生错误而是继续尝试其他候选函数
+// - 常用于根据类型特性选择不同的函数实现，是C++中实现"编译期多态"的重要机制
+
+// 以下示例展示如何使用SFINAE检测类型是否支持特定操作
+template <typename T>
+typename std::enable_if<std::is_integral<T>::value, bool>::type is_positive(T value)
+{
+  return value > 0;
+}
+
+// 启用仅当T是浮点类型时的函数
+template <typename T>
+typename std::enable_if<std::is_floating_point<T>::value, bool>::type is_positive(T value)
+{
+  return value > 0.0;
+}
+
+int main()
+{
+  // 1. 测试函数模板
+  std::cout << "Function template examples:" << std::endl;
+  std::cout << "max_value(10, 20): " << max_value(10, 20) << std::endl;
+  std::cout << "max_value(3.14, 2.71): " << max_value(3.14, 2.71) << std::endl;
+  std::cout << "max_value(\"apple\", \"banana\"): " << max_value<std::string>("apple", "banana") << std::endl;
+
+  // 2. 测试类模板
+  std::cout << "\nClass template examples:" << std::endl;
+  Container<int> int_container(42);
+  std::cout << "int_container.get_data(): " << int_container.get_data() << std::endl;
+
+  Container<double> double_container(3.14159);
+  std::cout << "double_container.get_data(): " << double_container.get_data() << std::endl;
+
+  // 3. 测试模板特化
+  std::cout << "\nTemplate specialization examples:" << std::endl;
+  Container<std::string> string_container("Hello Templates!");
+  std::cout << "string_container.get_data(): " << string_container.get_data() << std::endl;
+  std::cout << "string_container.length(): " << string_container.length() << std::endl;
+
+  // 4. 测试变参模板
+  std::cout << "\nVariadic template examples:" << std::endl;
+  std::cout << "sum(1): " << sum(1) << std::endl;
+  std::cout << "sum(1, 2, 3, 4, 5): " << sum(1, 2, 3, 4, 5) << std::endl;
+  std::cout << "sum(1.1, 2.2, 3.3): " << sum(1.1, 2.2, 3.3) << std::endl;
+
+  // 5. 测试SFINAE
+  std::cout << "\nSFINAE examples:" << std::endl;
+  // - 对于整数类型，调用的是以">0"判断正负的版本
+  std::cout << "is_positive(42): " << (is_positive(42) ? "true" : "false") << std::endl;
+  std::cout << "is_positive(-42): " << (is_positive(-42) ? "true" : "false") << std::endl;
+  // - 对于浮点类型，调用的是用">0.0"判断正负的版本
+  std::cout << "is_positive(3.14): " << (is_positive(3.14) ? "true" : "false") << std::endl;
+  std::cout << "is_positive(-3.14): " << (is_positive(-3.14) ? "true" : "false") << std::endl;
+
+  std::cout << "\npassed!" << std::endl;
+  return 0;
+}