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digitalmars.D - Catch div 0

reply mogu <mogucpp 163.com> writes:
Should d make div 0 a runtime exception? Or as an optional 
feature?
I never want my program crashes only beause of reading a wrong 
number from runtime configurations.
Jul 20 2019
parent reply Johannes Loher <johannes.loher fg4f.de> writes:
Am 20.07.19 um 19:31 schrieb mogu:

 Should d make div 0 a runtime exception? Or as an optional feature?
 I never want my program crashes only beause of reading a wrong number
 from runtime configurations.
 


I suggest you take a look at std.experimental.checkedint
(https://dlang.org/phobos/std_experimental_checkedint.html). It allows
you to specify what exact behavior you want to have on a very fine
granular level and also defines a few very useful presets, e.g. `Throw`,
which looks very much like you want:

```
import std.exception : assertThrown;
auto x = -1.checked!Throw;
assertThrown(x / 0);
```
Jul 20 2019
parent reply mogu <mogucpp 163.com> writes:
On Saturday, 20 July 2019 at 21:11:34 UTC, Johannes Loher wrote:

 Am 20.07.19 um 19:31 schrieb mogu:

 Should d make div 0 a runtime exception? Or as an optional 
 feature? I never want my program crashes only beause of 
 reading a wrong number from runtime configurations.
 


 I suggest you take a look at std.experimental.checkedint 
 (https://dlang.org/phobos/std_experimental_checkedint.html). It 
 allows you to specify what exact behavior you want to have on a 
 very fine granular level and also defines a few very useful 
 presets, e.g. `Throw`, which looks very much like you want:

 ```
 import std.exception : assertThrown;
 auto x = -1.checked!Throw;
 assertThrown(x / 0);
 ```


Thanks. But if I use checked int, I must let all my libs support 
checked int. Otherwise I must take care of all the parts using 
ints from checked in order to safely interacting with other libs.
As a designer, I wish other logic programmers will not break down 
the whole program suddenly. But now I have to use multi-process 
instead of only a single one to handle it.
Jul 20 2019
parent Johannes Loher <johannes.loher fg4f.de> writes:
On Sunday, 21 July 2019 at 01:59:53 UTC, mogu wrote:

 On Saturday, 20 July 2019 at 21:11:34 UTC, Johannes Loher wrote:

 Am 20.07.19 um 19:31 schrieb mogu:

 Should d make div 0 a runtime exception? Or as an optional 
 feature? I never want my program crashes only beause of 
 reading a wrong number from runtime configurations.
 


 I suggest you take a look at std.experimental.checkedint 
 (https://dlang.org/phobos/std_experimental_checkedint.html). 
 It allows you to specify what exact behavior you want to have 
 on a very fine granular level and also defines a few very 
 useful presets, e.g. `Throw`, which looks very much like you 
 want:

 ```
 import std.exception : assertThrown;
 auto x = -1.checked!Throw;
 assertThrown(x / 0);
 ```


 Thanks. But if I use checked int, I must let all my libs 
 support checked int. Otherwise I must take care of all the 
 parts using ints from checked in order to safely interacting 
 with other libs.
 As a designer, I wish other logic programmers will not break 
 down the whole program suddenly. But now I have to use 
 multi-process instead of only a single one to handle it.


I do not think the situation is as bad as you describe it. In 
particular the interaction of checked int with regular ints works 
reasonably well.

But yes, you are right, code written by others can still result 
in the whole program being stopped by SIGFPE.

For better or worse, checked int is the best solution you have. 
Throwing on division by 0 for regular ints will never get into D 
because that would mean that regular integer division (and modulo 
operation) is not nothrow anymore, which would prevent almost any 
code from being nothrow, rendering nothrow totally useless. Also 
it would make division slower because it would need to be checked 
in the language while currently the SIGFPE is basically raised by 
the processor.
Jul 21 2019