Comparison and application of C++ function templates and std::function?

Function templates and std::function are both ways to represent functions in C. They each have their own advantages and disadvantages: Function template: static type safety, excellent performance, but low flexibility and cannot store dynamic function objects. std::function: dynamic type safety, high flexibility, can store lambda expressions and functors, but has slightly poor performance and weak type safety. Use function templates in scenarios where static type safety is required and performance is paramount, and std::function when dynamic flexibility is required.

Comparison and application of C function template and std::function

Function template and std::function are all methods used to represent functions in C. They each have their own advantages and applicable scenarios.

Function template

• Features: Static type safety, compile-time analysis, small size.

• Advantages:

  • Excellent performance, the compiler is directly inlined.
  • Type safety to prevent errors at runtime.

• Disadvantages:

  • is not very flexible and is bound to specific function types at compile time.
  • Cannot store dynamic function objects such as lambda expressions or functors.

std::function

• Features:Dynamic type safety, runtime binding ,Big size.

• Advantages:

  • Very flexible and can store any callable object.
  • Supports lambda expressions and functors.

• Disadvantages:

  • Performance is slightly lower than function templates because type conversion is required at runtime.
  • Type safety is weak and type errors may occur at runtime.

Compare

##FeaturesFunction Templatestd::functionType safetystaticdynamicPerformanceExcellentSlightly worseFlexibilityLowHighVolumeSmallLarge##Practical case

Use function template:

template<typename T>
double sum(vector<T> &numbers) {
  double total = 0;
  for (T num : numbers) {
    total += num;
  }
  return total;
}

Use std::function:

// 创建一个存储 lambda 表达式的 function 对象
std::function<double(vector<int> &)> sum = [](vector<int> &numbers) -> double {
  double total = 0;
  for (int num : numbers) {
    total += num;
  }
  return total;
};

Application scenario

• Function template:
  When static type safety is required and performance is paramount (for example, math library).
  • When the function type is known and unchanged.
• std::function:
  When dynamic flexibility is required, such as storing lambda expressions or functors.
  • When the function type may change at runtime.

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