https://issues.dlang.org/show_bug.cgi?id=17746
--- Comment #1 from Jack Stouffer <j...@jackstouffer.com> --- >From my initial investigation into this, adding ref counting to BigInt is much more complicated than it first appears. Adding a size_t ref count on the heap for BigUint basically breaks the rest of BigInt because anytime BigInt is const/immutable it makes the pointer to the reference count const/immutable as well. Meaning, const(BigInt) is no longer implicitly convert-able to BigInt. I'm not sure this is doable without a large rewrite. --