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SubjectRe: block: new gcc-5.1 warnings..
From
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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