Once, I wanted to write a C# function roughly like this:

  (T1, ..., Tn) Apply<T1, ..., Tn>((Func<P, T1>, ..., Func<P, Tn>) args)

This is not possible in C# because the language doesn't have variadic generics. Instead, I used runtime reflection and wrote something like this:

  object[] Apply(Func<P, object>[] args)

Although it worked, the downside is that the types T1, ..., Tn are no longer statically known, which means that the function's contract has to be written in comments and the caller has to check them manually. In contrast, C++ has variadic templates, which would allow the compiler to check the types automatically.