CODEWITHSUNDEEP
c++templateslambdatemplate-meta-programming
Setu
Setu

Reputation: 1002

Lambdas as non-type template parameters

Consider the following code:

#include <iostream>

template<auto lambda>
auto execute()
{
    return lambda();
}

int main()
{
    auto no_capture = [](){
        std::cout << "Hello World\n";
    };

    const int local_var = 42;
    auto capture_by_value = [=](){
        std::cout << "Hello World " << local_var << '\n';
    };

    auto capture_by_reference = [&](){
        std::cout << "Hello World " << local_var << '\n';
    };

    execute<no_capture>();
    execute<capture_by_value>();
    execute<capture_by_reference>();

    return 0;
}

This code compiles and executes as expected. Here's the link to compiler explorer.

I want to specialize the the templated function execute such that it only accepts one of the three lambdas. In other words, I want to restrict the acceptable template parameters to lambdas which (1) do not capture anything, or (2) only capture variables by value, or (3) only capture variables by reference. I want to know how can I enforce these restrictions using template meta-programming.

Upvotes: -3

Views: 97

Answers (0)

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