import std.range; void main() { iota(1, 2_147_483_648); } outputs: src/phobos/std/range.d(2154): Error: cannot implicitly convert expression (aBitAboveCount) of type long to uint
I can't reproduce this on the current SVN version of Phobos. Iota has been majorly debugged lately. What version of DMD/Phobos are you using?
update to dmd 2.028 fixes this bug.