Re: [Boost-users] Ugly warnings from BOOST_STATIC_ASSERT

From: Erik (esigra_at_[hidden])
Date: 2008-03-18 11:05:09

Nat Goodspeed skrev:
> Erik wrote:
>   
>> John Maddock skrev:
>>     
>>> Erik wrote:
>>>   
>>>       
>>>> We have this really neat and simple macro in our project:
>>>> #define compile_assert(x) typedef bool COMPILE_ASSERT[(x) ? 1 : -1]
>>>>
>>>> Although it does what we need and serves us well, I tried to replace
>>>> it with BOOST_STATIC_ASSERT. Unfortunately this resulted in a lot of
>>>> ugly warnings throughout the compile:
>>>>   warning: use of old-style cast
>>>>     
>>>>         
>>> Which compiler is this?
>>>   
>>>       
>> g++ (with the parameter -Wold-style-cast)
>>     
>
> I bet he's going to ask you which version of g++ you're using. Behavior 
> can vary widely across versions.

I do not think so. An old-style-cast is a well-defined thing and all 
versions of g++ that has -Wold-style-cast should catch them. The only 
thing that varies between versions is that g++-4.2 and later also have 
-Werror=old-style-cast.

Note: This is what the creator of C++ has to say about old-style-cast:
«From C, C++ inherited the notation (T) e, which performs any conversion 
that can be expressed as a combination of static_casts, 
reinterpret_casts, and const_casts to make a value of type T from the 
expression e (§B.2.3). This C-style cast is far more dangerous than the 
named conversion operators because the notation is harder to spot in a 
large program and the kind of conversion intended by the programmer is 
not explicit. That is, (T) e might be doing a portable conversion 
between related types, a nonportable conversion between unrelated types, 
or removing the const modifier from a pointer type. Without knowing the 
exact types of T and e, you cannot tell.» (Stroustrup, 2000)