Re: rational.hpp: !!m? no way, jose!

From: Dean Sturtevant (deansturtevant_at_[hidden])
Date: 2001-01-11 23:51:19

I agree with the Stephen that the statement "while (m)" is 
inappropriate. m is an integer type, not a boolean. There's no need 
to provide operator!, which contrives to treat m like a boolean. 
Instead, you want comparison with 0, or perhaps more principled, a 
default-constructed item of the type. That is, the line should read

"while (m != 0)" or "while (m != IntType())", assuming the latter 
construct is legal C++. And the comparison within the algorithm is a 
little strange: Why would n % m be < 0 ? I would have thought that 
any reasonable def of '%' would always yield non-negative numbers?

--- In boost_at_[hidden], "Stephen Silver" <boost_at_a...> wrote:

> The first problem is fairly minor.  The gcd() function template in
> rational.hpp is documented as working for "any types for which the
> following operations are defined: =, +=, *=, /=, %, <".  However, it
> contains the line
> 
>     while (m) {
> 
> so it also requires that implicit conversion to bool be possible.  
This
> is not a very desirable requirement, because user-defined conversion
> functions that convert to built-in types are not very safe (due to 
the
> possibility of the conversion happening in contexts where it was not
> anticipated).  Note that the above line could be changed to
> 
>     while (!!m) {
> 
> which would have the advantage that it could work by means of 
operator!
> instead of requiring implicit conversion to bool.
>