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Re: Implementing static_assert

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jacobnavia wrote:
> Le 07/05/2015 12:13, Ian Collins a écrit :
>> David Brown wrote:
>>>
>>> I /strongly/ disapprove of the idea of turning the static assert into a
>>> run-time call if it can't be evaluated at compile-time.  I am not as
>>> experienced a "language lawyer" as Keith and some of the others here,
>>> but I believe the C11 standards insist that the boolean expression be
>>> compile-time constant - and I certainly think that /should/ be the case.
>>>    It is in the name - it is a /static/ assertion, and should have a
>>> /static/ effect.  So no matter what freedom the C11 standard may or may
>>> not give, give an error message if the expression is not constant.
>>
>> I completely agree.  If the programmer doesn't realise the expression
>> can't be evaluated at compile time, they could be lulled into a false
>> sense of security.  A static_assert should fail a compile time, it is
>> likely to be used to check the sanity of a build environment.  One
>> example would be a continuous integration build that is built but never
>> run.
>>
>
> 1: If the expression fails at compile time an error is issued and
> compilation fails.
>
> 2: If the expression is not a constant expression, code is generated to
> evaluate it at run time. The objective of that was to replace assert by
> static assert, and (if possible) test all the asserts at compile time to
> produce an error message at compile time if possible.
>
> For instance
>
> assert(sizeof(void *) == 4)
>
> would be tested at run time even if it could be done at compile time.
>
> But aparently everyone agrees that that is an error...

It isn't an error, it is what assert does.

What static_assert does is completely different, this is a good example 
of a use case for static_assert.  As David mentions, it would make sense 
for asserts of compile time constants to be evaluated at compile time, 
not the other way.

If I write a static_assert in my code, I want it to fail to build if the 
condition isn't met.  As part of out continuous integration process, I 
build out embedded targets with the ARM-gcc tool chain as part of each 
build.  These builds are never run, so a static_assert that doesn't do 
what is says on the tin is worse than useless.

-- 
Ian Collins

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Thread

Implementing static_assert jacobnavia <jacob@jacob.remcomp.fr> - 2015-05-06 21:44 +0200
  Re: Implementing static_assert Keith Thompson <kst-u@mib.org> - 2015-05-06 13:28 -0700
    Re: Implementing static_assert jacobnavia <jacob@jacob.remcomp.fr> - 2015-05-06 22:55 +0200
      Re: Implementing static_assert Keith Thompson <kst-u@mib.org> - 2015-05-06 14:30 -0700
        Re: Implementing static_assert Martin Shobe <martin.shobe@yahoo.com> - 2015-05-06 18:07 -0500
          Re: Implementing static_assert Keith Thompson <kst-u@mib.org> - 2015-05-06 17:34 -0700
          Re: Implementing static_assert David Brown <david.brown@hesbynett.no> - 2015-05-07 09:44 +0200
      Re: Implementing static_assert Tim Rentsch <txr@alumni.caltech.edu> - 2015-05-07 12:37 -0700
  Re: Implementing static_assert David Brown <david.brown@hesbynett.no> - 2015-05-07 10:11 +0200
    Re: Implementing static_assert Ian Collins <ian-news@hotmail.com> - 2015-05-07 22:13 +1200
      Re: Implementing static_assert jacobnavia <jacob@jacob.remcomp.fr> - 2015-05-07 12:24 +0200
        Re: Implementing static_assert Ian Collins <ian-news@hotmail.com> - 2015-05-07 22:33 +1200
          Re: Implementing static_assert David Brown <david.brown@hesbynett.no> - 2015-05-07 14:30 +0200
    Re: Implementing static_assert Philip Lantz <prl@canterey.us> - 2015-05-07 03:53 -0700
      Re: Implementing static_assert David Brown <david.brown@hesbynett.no> - 2015-05-07 14:21 +0200
        Re: Implementing static_assert Keith Thompson <kst-u@mib.org> - 2015-05-07 09:11 -0700
          Re: Implementing static_assert James Kuyper <jameskuyper@verizon.net> - 2015-05-07 12:30 -0400
            Re: Implementing static_assert James Kuyper <jameskuyper@verizon.net> - 2015-05-07 12:55 -0400
    Re: Implementing static_assert Keith Thompson <kst-u@mib.org> - 2015-05-07 09:06 -0700
  Re: Implementing static_assert jacobnavia <jacob@jacob.remcomp.fr> - 2015-05-07 19:43 +0200
    Re: Implementing static_assert Tim Rentsch <txr@alumni.caltech.edu> - 2015-05-07 16:10 -0700

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