I have to execute several lambda functions, but every each N
lambdas a prologue()
function also must be run. The number of lambdas can be arbitrary large and N
is known at compile time. Something like this:
static void prologue( void )
{
cout << "Prologue" << endl;
}
int main()
{
run<3>( // N = 3
[](){ cout << "Simple lambda func 1" << endl; },
[](){ cout << "Simple lambda func 2" << endl; },
[](){ cout << "Simple lambda func 3" << endl; },
[](){ cout << "Simple lambda func 4" << endl; },
[](){ cout << "Simple lambda func 5" << endl; },
[](){ cout << "Simple lambda func 6" << endl; },
[](){ cout << "Simple lambda func 7" << endl; }
);
}
outputs:
Prologue
Simple lambda func 1
Simple lambda func 2
Simple lambda func 3
Prologue
Simple lambda func 4
Simple lambda func 5
Simple lambda func 6
Prologue
Simple lambda func 7
End
Remainders must be handled properly.
I have reached the following solution, but as you can see it is not very scalable because I have to write a handler for each N
!
It is possible to do some magic meta-programming to cover every possible N
? Have I lost the focus and there is a completely different approach to solve this problem? Everything must be resolved at compile time.
#include <iostream>
using namespace std;
static void prologue( void );
// Primary template
template< int N, typename... Args>
struct Impl;
// Specialitzation for last cases
template< int N, typename... Args >
struct Impl
{
static void wrapper( Args... funcs )
{
Impl<N-1, Args...>::wrapper( funcs... );
}
};
// Specilitzation for final case
template<int N>
struct Impl<N>
{
static void wrapper( )
{
cout << "End" << endl;
}
};
template< typename Arg1, typename... Args >
struct Impl<1, Arg1, Args...>
{
static void wrapper( Arg1 func1, Args... funcs )
{
prologue();
func1();
Impl<1, Args...>::wrapper( funcs... );
}
};
template< typename Arg1, typename Arg2, typename... Args >
struct Impl<2, Arg1, Arg2, Args...>
{
static void wrapper( Arg1 func1, Arg2 func2, Args... funcs )
{
prologue();
func1();
func2();
Impl<2, Args...>::wrapper( funcs... );
}
};
template< typename Arg1, typename Arg2, typename Arg3, typename... Args >
struct Impl<3, Arg1, Arg2, Arg3, Args...>
{
static void wrapper( Arg1 func1, Arg2 func2, Arg3 func3, Args... funcs )
{
prologue();
func1();
func2();
func3();
Impl<3, Args...>::wrapper( funcs... );
}
};
// Static class implementation wrapper
template< int N, typename... Args >
static void run( Args... funcs )
{
Impl<N, Args...>::wrapper( funcs... );
}
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