Re: [boost] Digest Number 365

From: Beman Dawes (bdawes_at_[hidden])
Date: 2001-01-12 19:52:03

At 04:05 PM 1/12/2001 -0500, George A. Heintzelman wrote:
 > ...
 >> Yes, but I don't really see any problems with it, other than the
 >> efficiency issue with certain bigint types.  In cases where the
 >> efficiency is a real issue, the template constructor can be by-passed
 >> by using an explicit cast to IntType.
 >
 >This is where you need an implicit_cast template:
 >
 >template <class ToClass, class FromClass>
 >ToClass implicit_cast(const FromClass &casted_object)
 >	{ return casted_object; }
 >
 >which will not compile unless there is an implicit conversion from
 >FromClass to ToClass. Then the constructor becomes:
 >
 >template <class T> rational(T n) :
 >	num(boost::implicit_cast<IntType>(n)),
 >	den(IntType(1)) {} // Or whatever you finally decide to use for 1.
 >
 >I seem to remember some discussion about exactly this sort of need, and
 >had thought that it was in the BCL, but it doesn't seem to be. Perhaps
 >this is an example which suggests it needs to be added?

We removed implicit_cast<> because it had a number of problems.  The 
comment in the header says:

// Removed due to uncertain purpose. Use either numeric_cast (see below)
// or static_cast according to the need.

Best,

--Beman