How Can Generic Lambdas Be Converted to std::functions Using Templates in C ?

Converting Lambdas to std::functions Using Templates

Introduction:

Lambda expressions provide a concise and convenient way to define anonymous functions in C . However, when working with variadic templates, passing lambdas can be challenging. This article explores a technique to convert generic lambdas into std::functions using template metaprogramming.

Template-Based std::function Conversion:

To enable the conversion of a lambda with arbitrary parameters to an std::function, we cannot rely on template type deduction. Instead, we employ an identity type to wrap the lambda function and preserve its type information:

template <typename T>
struct identity
{
  typedef T type;
};

Using this identity type, we create a generic function that accepts the wrapped lambda as an argument:

template <typename... T>
void func(typename identity<std::function<void(T...)>>::type f, T... values) {
  f(values...);
}

Example Usage:

While this approach does not require explicitly specifying template parameters, it involves passing additional arguments to the function. Here's an example:

func([](int x, int y, int z) { std::cout << (x*y*z) << std::endl; }, 3, 6, 8);

Conclusion:

While this solution addresses the challenge of converting generic lambdas to std::functions in the context of variadic templates, it does require the passing of additional arguments. Alternatively, one can use explicit template parameter specification or consider alternative approaches such as using function pointers or a function-object wrapper.

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