Ruby factorial function

Question

I\'m going crazy: Where is the Ruby function for factorial? No, I don\'t need tutorial implementations, I just want the function from the library. It\'s not in Math!

Answer 1

With high respect to all who participated and spent their time to help us, I would like to share my benchmarks of the solutions listed here. Params:

iterations = 1000

n = 6

                                     user     system      total        real
Math.gamma(n+1)                   0.000383   0.000106   0.000489 (  0.000487)
(1..n).inject(:*) || 1            0.003986   0.000000   0.003986 (  0.003987)
(1..n).reduce(1, :*)              0.003926   0.000000   0.003926 (  0.004023)
1.upto(n) {|x| factorial *= x }   0.003748   0.011734   0.015482 (  0.022795)

For n = 10

  user     system      total        real
0.000378   0.000102   0.000480 (  0.000477)
0.004469   0.000007   0.004476 (  0.004491)
0.004532   0.000024   0.004556 (  0.005119)
0.027720   0.011211   0.038931 (  0.058309)