[Issue 17736] bigint opunary should be better performing

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=17736

hsteoh at quickfur.ath.cx changed:

           What    |Removed                     |Added
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                 CC|                            |hsteoh at quickfur.ath.cx

--- Comment #1 from hsteoh at quickfur.ath.cx ---
I notice also that binary operators on BigInt (even the opOpAssign ones like
+=) will create new instances of BigInt rather than update in-place.

One trouble with updating in-place is that it makes BigInt assignment either
expensive (always copy) or exhibit reference semantics:

---
BigInt x = 1;
BigInt y = x;
++y;
writeln(x); // will this print 1 or 2?
---

If I understand the BigInt design correctly, reference semantics are *not*
desirable because we want BigInt to be more-or-less a drop-in replacement of
fixed-size ints, and lots of code will break in subtle ways if the by-value
semantics was substituted with by-reference semantics.

One thought is that if BigInt uses some sort of reference-counting scheme, then
if the refcount is 1 we can update in-place, otherwise allocate a new BigInt to
hold the result as usual.

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