On 10/7/19 9:30 PM, Junio C Hamano wrote:
> SZEDER Gábor <szeder.dev@xxxxxxxxx> writes:
>
>>> func(PROGRESS | REGRESS);
>>> func(PROGRESS + REGRESS);
>>> func(PROGRESS * 3);
>>> }
>>>
>>> how caller came about to give 3?
>>
>> No, they tend to show (PROGRESS | REGRESS), at least both gdb and lldb
>> do.
>
> OK.
>
>> If the enum has only constants with power-of-two values, then that
>> is the right way to write it, and the other two are asking for trouble
>
> If the programmer and the debugger knows the constants are used to
> represent bits that can be or'ed together, what you say is correct,
> but that is entirely irrelevant.
>
> What I was worried about is that the constants that are used to
> represent something that are *NOT* set of bits (hence "PROGRESS * 3"
> may be perfectly a reasonable thing for such an application) may be
> mistaken by an overly clever debugger and "3" may end up getting
> shown as "PROGRESS | REGRESS". When there are only two constants
> (PROGRESS=1 and REGRESS=2), we humans nor debuggers can tell if that
> is to represent two bits that can be or'ed together, or it is an
> enumeration.
>
> Until we gain the third constant, that is, at which time the third
> one may likely be 3 (if enumeration) or 4 (if bits).
>
I tried to see how lldb would handle the "PROGRESS * 3" scenario
but I was unable to get lldb to display the "PROGRESS | REGRESS" format
even when ORing the flags:
(lldb) l 399
399 enum test_flags {
400 TEST_FLAG_1 = 1 << 0,
401 TEST_FLAG_2 = 1 << 1,
402 };
403
404 enum test_flags flags_1 = TEST_FLAG_1;
405 enum test_flags flags_2 = TEST_FLAG_2;
406 enum test_flags flags_both = TEST_FLAG_1 | TEST_FLAG_2;
407
408 if (flags_1 || flags_2 || flags_both)
(lldb) p flags_1
(test_flags) $0 = TEST_FLAG_1
(lldb) p flags_2
(test_flags) $1 = TEST_FLAG_2
(lldb) p flags_both
(test_flags) $2 = 3
(lldb) fr v flags_both
(test_flags) flags_both = 3
(lldb) fr v --format enum flags_both
(test_flags) flags_both = 3
(lldb) version
lldb-902.0.79.7
Swift-4.1
Is there something that needs to be adjusted in the config or with
--format to display "TEST_FLAG_1 | TEST_FLAG_2" in this example?
Thanks,
William
