On Friday, 13 March 2015 at 12:49:48 UTC, Dennis Ritchie wrote:
On Friday, 13 March 2015 at 02:38:18 UTC, Rikki Cattermole
wrote:
You could assign it to e.g. an enum. Or force it over using
meta-programming.
And this code can be rewritten to D?
template <int n>
struct Factorial
{
enum { value = n * Factorial<n - 1>::value };
};
template <>
struct Factorial<0>
{
enum { value = 1 };
};
int main()
{
constexpr auto x = Factorial<5>::value;
constexpr auto y = Factorial<7>::value;
}
You can translate it directly:
template Factorial(int n)
{
static if (n == 0)
{
enum Factorial = 1;
}
else static if (n > 0)
{
enum Factorial = n * Factorial!(n - 1);
}
else
{
static assert(false, "n cannot be negative");
}
}
int main()
{
//Calculated at compile time
auto x = Factorial!5;
auto y = Factorial!7;
}
However, it's much easier to just write a function and decide
whether you want to calculate its value at runtime or compile
time.
int factorial(int n)
in
{
assert(n >= 0, "n cannot be 0");
}
body
{
return n == 0 ? 1 : n * factorial(n - 1);
}
void main()
{
//Evaluated at compile time
enum x = factorial(5);
//Evaluated at runtime
auto y = factorial(7);
}