C#•2mo ago

Creating a method that takes a generic method and its variadic parameters as arguments and call it i

I need a way to pass generic static methods and its argument to another method, and the static method inside this another method. In C++, I can easily achieve this with variadic templates and std::forward:

#include <utility>
#include <cstdio>

template <typename Func, typename... Args>
void actual_call_func(Func func, Args &&...args) {
    func(std::forward<Args>(args)...);
}

int main() {
    auto func = std::printf;
    constexpr const char* param_0 = "%d + %d = %d";
    int param_1 = 3;
    int param_2 = 4;
    int param_3 = 3 + 4;

    actual_call_func(func, param_0, param_1, param_2, param_3);
}

#include <utility>
#include <cstdio>

template <typename Func, typename... Args>
void actual_call_func(Func func, Args &&...args) {
    func(std::forward<Args>(args)...);
}

int main() {
    auto func = std::printf;
    constexpr const char* param_0 = "%d + %d = %d";
    int param_1 = 3;
    int param_2 = 4;
    int param_3 = 3 + 4;

    actual_call_func(func, param_0, param_1, param_2, param_3);
}

But I don't know how to do this easily in C#; Previously I just captured all the required arguments into a lambda, which calls the static method inside of it, and passed it as an single Action.

// Let's just pass this to the actual call function
Action call = () => { Console.WriteLine(param0, param1); };

// Let's just pass this to the actual call function
Action call = () => { Console.WriteLine(param0, param1); };

But this breaks when I have non-capturable arguments such as Span<T>. And I don't want to use params object[]? to box the arguments. The only way I can think of is declaring the ActualCallFunc one by one:

void ActualCallFunc(Action func);
void ActualCallFunc<T>(Action<T> func, T param0);
void ActualCallFunc<T0, T1>(Action<T0, T1> func, T0 param0, T1 param1);
void ActualCallFunc<T0, T1, T2>(Action<T0, T1, T2> func, T0 param0, T1 param1, T2 param2);
...

void ActualCallFunc(Action func);
void ActualCallFunc<T>(Action<T> func, T param0);
void ActualCallFunc<T0, T1>(Action<T0, T1> func, T0 param0, T1 param1);
void ActualCallFunc<T0, T1, T2>(Action<T0, T1, T2> func, T0 param0, T1 param1, T2 param2);
...

But not only this is cumbersome, it would not work if sometimes the parameter needs to use ref. Is there any nice way to solve this like in C++?

9 Replies

Angius•2mo ago

C# has no variadic generic parameters There is a source generator I see, written by @WhiteBlackGoose: https://github.com/WhiteBlackGoose/InductiveVariadics A proposal has been made in 2015: https://github.com/dotnet/roslyn/issues/5058

yeonOP•2mo ago

Hmm, too bad it is not a thing. Source generator approach looks interesting, but I think it's a bit overkill solution for my usecase Hmm, I'll just declare these manually for now then

Angius•2mo ago

You could do some fucky-wucky stuff with delegates, if you really must

MODiX•2mo ago

Angius

sharplab.io (click here)

void Call(Delegate d, object data) {
    d.DynamicInvoke(data);
}
Call((string s) => Console.Write(s), "hello");

void Call(Delegate d, object data) {
    d.DynamicInvoke(data);
}
Call((string s) => Console.Write(s), "hello");

Try the /sharplab command! | React with ❌ to remove this embed.

yeonOP•2mo ago

Hmm, I believe this DynamicInvoke also boxes the parameters, I would like to avoid that if possible Thanks for suggesting, anyways

Anton•2mo ago

put your parameters in a struct this kind of pattern in C# is a burden to maintain

WhiteBlackGoose•2mo ago

did it pop up on your search engine?

Angius•2mo ago

WhiteBlackGoose•2mo ago

cool 😄

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Creating a method that takes a generic method and its variadic parameters as arguments and call it i

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