Re: [boost] [mpl] clang error for narrowing from unsigned int 0xffffffff to long

Subject: Re: [boost] [mpl] clang error for narrowing from unsigned int 0xffffffff to long
From: Jonathan Wakely (jwakely.boost_at_[hidden])
Date: 2013-11-14 05:09:59

On 14 November 2013 10:09, Jonathan Wakely wrote:
> On 14 November 2013 04:22, Edward Diener wrote:
>> On 11/13/2013 5:37 PM, Jonathan Wakely wrote:
>>>
>>> You can use an explicit conversion, e.g. (long)0xffffffff
>>
>>
>> Or my own preference of 'static_cast<long>(0xffffffff)'. But using
>
> Yep, that's equivalent, and arguably clearer and cleaner.
>
>> '0xffffffffL' does not work. I admit that understanding the C++ Standard's
>> different interprtetation of these two forms is beyond me.
>
> The expression static_cast<long>(0xffffffff) has type long, the
> expression 0xffffffff

Oops, I meant 0xffffffffL here ...

> has a type given by [lex.icon], which on a
> 32-bit system will be unsigned long.  Using that expression as a
> non-type template argument (14.3.2 [temp.arg.nontype] p5) requires no
> conversion for the former, but requires an implicit conversion from
> unsigned long to long in the latter case, and since the value would
> change that is a narrowing conversion, which is not allowed in a
> converted constant expression (5.19 [expr.const] p3).