Messages in this thread | | | Date | Wed, 27 May 2015 16:34:51 -0700 | Subject | Re: block: new gcc-5.1 warnings.. | From | Linus Torvalds <> |
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On Wed, May 27, 2015 at 4:18 PM, Linus Torvalds <torvalds@linux-foundation.org> wrote: > So I do actually agree that > > switch (boolean) { > case non-boolean: > > can very much be worth a warning. But then it's about type-safety > issues, rather than about "you shouldn't use switch() with a boolean".
Btw, I'd actually like to see (possibly optionally) a warning for enum types there too. Exactly because *type* based warnings very much make sense, regardless of number of cases.
For example, try this:
#include <stdbool.h> #include <stdio.h>
enum a { one, two };
int t(bool b, enum a e) { switch (b) { case true: printf("No arguments\n"); /* fallthrough */ case false: printf("\n"); }
switch (e) { case 0: printf("one"); break; case two: printf("two"); break; } return 0; }
and I'd argue that gcc-5.1 warns about TOTALLY THE WRONG THING.
It does that *stupid* warning:
warning: switch condition has boolean value [-Wswitch-bool]
which is just idiotic and wrong.
The case statements are clearly boolean, there is absolutely nothing wrong with that switch, and a compiler that warns about it is just being f*cking moronic.
In contrast, that second switch() statement with the "case 0:" is actually something that might well be worth warning for. I'd argue that the code would clearly be more legible if it used "case one:" instead.
So the new warning in gcc-5 seems to be just stupid. In general, warnings that encourage you to write bad code are stupid. The above
switch (boolean) { case true:
is *good* code, while the gcc documentation suggests that you should cast it to "int" in order to avoid the warning, but anybody who actually thinks that
switch ((int)boolean) { switch 1:
is better, clearly has absolutely zero taste and is just objectively wrong.
Really. A warning where the very *documentation* tells you to do stupid things is stupid.
Linus
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