Bug 7646 – bug in code sample and unittest

The following sample code on std.functional contains a bug. http://dlang.org/phobos/std_functional.html#memoize ulong fib(ulong n) { alias memoize!fib mfib; return n < 2 ? 1 : mfib(n - 2) + mfib(n - 1); } assert(fib(10) == 89); fib(10) should be 55. http://en.wikipedia.org/wiki/Fibonacci_number#List_of_Fibonacci_numbers I think the code should be (n <= 2): ulong fib(ulong n) { alias memoize!fib mfib; return n <= 2 ? 1 : mfib(n - 2) + mfib(n - 1); } assert(fib(10) == 55); It's also in the unittest https://github.com/D-Programming-Language/phobos/blob/master/std/functional.d

(In reply to comment #0) > I think the code should be (n <= 2): > > ulong fib(ulong n) { > alias memoize!fib mfib; > return n <= 2 ? 1 : mfib(n - 2) + mfib(n - 1); > } > > assert(fib(10) == 55); No, that still won't do. This is better: ulong fib(ulong n) { alias memoize!fib mfib; return n <= 2 ? n != 0 : mfib(n - 2) + mfib(n - 1); }

ulong fib (ulong n) { alias memoize!fib mfib; return n < 2 ? n : mfib(n - 2) + mfib(n - 1); }

It turns out some people regard F0 = 0 and some F0 = 1. So it's not a bug after all.