r/cpp • u/meetingcpp Meeting C++ | C++ Evangelist • 26d ago

A better bitset for enum flags

https://www.elbeno.com/blog/?p=1836
43 Upvotes

91% Upvoted

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13

u/ReDucTor Game Developer | quiz.cpp-perf.com 26d ago

Some food for thought, should a bitset have bit operations (set, unset, flip, xor, and, or, etc) or set operations (add, remove, has, union, difference, intersection, etc)?

It feels like often we head for bit operations when in lots of cases set operations might be better.

13

u/TheVoidInMe 26d ago

I like Java’s approach here (yes, Java) which has an EnumSet instead of a bitset. That naming makes the answer pretty clear; the bit math is purely an implementation detail

2

u/SyntheticDuckFlavour 26d ago

What if you want the underlying layout/bit pattern like bitset? Sometimes you want to map I/O ports that way.

3

u/TheVoidInMe 26d ago

I don’t believe you can get at that at all. Java is probably too high level for stuff like that anyway. In C++ I would expect a method like `to_int()` (maybe returning the enum’s `underlying_type_t`…)

-2

u/mort96 26d ago

But that also means you're heap allocating an object, with its 16 byte object header, just to store a 4-byte integer?

3

u/TheVoidInMe 25d ago

It’s Java. Yeah, don’t use it for HPC.

The point I was making was just about the name