Re: [boost] Compile-time assert

From: Johan Paulsson (boost.org_at_[hidden])
Date: 2006-11-09 09:38:36

John Maddock wrote:
> Johan Paulsson wrote:
>> I wrote:
>>> Below is the compile-time assert I use.
>>> Would it be a useful addition to Boost?

8>< snip

> Frankly it's hard to choose between them on error message quality (which is 
> to say none are all that good).
> 
> One of the requirements that came up for static asserts when 
> BOOST_STATIC_ASSERT was talked about was a declaration like syntax, in fact 
> both:
> 
> static_assert<condition> x;
> 
> and
> 
> typedef static_assert<condition> x;
> 
> were explicitly rejected at the time.

Thank you for looking. I prefer some kind of template, but I now realize 
most do not.

> I also seem to remember that some compilers at the time evaluated typedefs 
> in a lazy manner: if the typedef was unused then it was never evaluated and 
> the static-assertion was never triggered.  That's the reason for some of the 
> convolutions inside static_assert.hpp.  I suspect, however, that current 
> compilers have moved away from such "lazyness".

That would make my implementation useless.

I think it would be interesting to know that a compile-time assert 
should work on any standard-conforming compiler. I don't know if, for 
example, typedef-ining an invalid type inside a function, and then not 
using the type, makes the program "ill formed" and requires a 
"diagnostic message".

Maybe the complie-time asserts in Boost should work on any 
standard-conforming compiler. I think that would be a good reason to use 
Boost and not mine.

/Johan Paulsson