What are the limitations of C++ lambda expressions?

C++ Lambda expressions have limitations, including: 1. Capture scope restrictions: only local variables in the definition scope can be accessed. 2. Type derivation limitation: the return type cannot be deduced from the body. 3. Universality limitation: cannot be templated. 4. Performance overhead: The performance overhead is greater than that of ordinary functions. 5. Difficulty in debugging: separation of definition and call location. Therefore, when using lambda expressions, you need to consider its limitations.

Limitations of C++ Lambda Expressions

Lambda expressions are a powerful tool in C++ that allow running Create an anonymous function. However, lambda expressions also have some limitations:

1. Capture scope

Lambda expressions can only capture local variables in their definition scope. That is, lambda expressions cannot access external functions or private members of a class.

2. Type derivation

The return type in a lambda expression cannot be deduced from its body like an ordinary function. This makes it difficult to type-check overloaded lambda expressions.

3. Universality

Lambda expressions cannot be templated. This limits their reusability and can lead to code duplication.

4. Performance overhead

Lambda expressions usually have greater performance overhead than ordinary functions. This is because lambda objects need to be created and destroyed at runtime.

5. Debugging Difficulty

Lambda expressions can be difficult to debug in a debugger because their definition is separated from the call site.

Practical case:

The following code demonstrates the limitations of lambda expressions:

#include <iostream>
#include <vector>

int main() {
  // 捕获范围限制 
  int x = 10;
  auto lambda = [x](int y) { return x + y; };
  // 无法访问外部变量y
  std::cout << lambda(20) << std::endl; // 编译错误

  // 类型推导限制
  // 无法从lambda主体中推导返回类型
  auto lambda2 = [](int x, int y) { return x > y ? x : y; };
  std::cout << lambda2(10, 20) << std::endl; // 编译错误

  // 通用性限制
  // 无法模板化lambda表达式
  // 以下代码会导致编译错误
  //template <typename T>
  //auto lambda3 = [](T x, T y) { return x + y; };

  // 性能开销限制
  // 循环调用lambda表达式会比调用普通函数慢
  std::vector<int> vec = {1, 2, 3, 4, 5};
  auto lambda4 = [](int x) { return x * x; };
  for (int i = 0; i < vec.size(); i++) {
    std::cout << lambda4(vec[i]) << " ";
  }
  std::cout << std::endl;

  return 0;
}

In the above example:

• Capture scope restriction: lambda expression lambda cannot access external variable y.
• Type derivation restriction: The return type of lambda expression lambda2 cannot be deduced from its body.
• Universality limitations: Lambda expressions cannot be templated.
• Performance overhead limitation: Looping a lambda expression lambda4 is slower than calling a normal function.

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