On Mon, Oct 14, 2019 at 11:27:54AM -0700, Jonathan Tan wrote: > > Jonathan Tan <jonathanta...@google.com> writes: > > > > >> > Also, I have a slight preference for putting "= 02" on the BLAME_COPY > > >> > line but that is not necessary. > > >> > > >> That is absolutely necessary; it is not like "we do not care what > > >> exact value _COPY gets; it can be any value as long as it is _MOVE > > >> plus 1", as these are used in set of bits (and again, I do not think > > >> it is such a brilliant idea to use enum for such a purpose). > > > > > > Good point. > > > > Doesn't that also show that enums are not quite a good fit for set > > of bits (i.e. 1<<n)? > > Well, I agree that it could be better, but with the C language as we > have it now, I still slightly prefer an enum to a list of #define. Both > ways, we still have to manually enter values for each flag, but with > enum, we get better debugger display (at least in gdb) and in the > function declaration and definition, we can put a specific type (instead > of "unsigned" or "int").
And then with any halfway decent editor (i.e. with ctags support) we can jump to the definition of that enum, see all the constants and read the comments. A proper IDE might even display all that as a tooltip when hovering over. > gdb supports the notion that a few people use > enums this way too, but if we decide as a project to not use enums in > this way, that's fine too. In a curious coincidence, today we celebrate the 12th anniversary of Git starting using an enum as a set of bitflags. Yay! :) > For what it's worth, I tried doing a search > online, but most of the results I got was for C# (where it is > recommended - they have a "[Flags]" attribute for enums), so maybe I am > indeed in the minority. I looked around among the various sources I have lying around, and found enums used as a set of bitflags in libgit2, linux, gcc, glibc, curl, vim, dash (but not Bash :). Anyway. Using an enum for a set of related bitflags has some very practical benefits. OTOH, I'm still not sure what its drawbacks are, especially what those drawbacks are that outweight the benefits.
