[boost] Re: zero and one

From: jsiek_at_[hidden]
Date: 1999-12-03 19:09:03

That solves a different problem than the one I was think of :)
I'll elaborate.

Suppose you're writing a generic algorithm, and need to call one
of the STL operations that takes an initial value, like accumulate.
Right now I would write something like this:

accumulate(start, finish, times<T>(), T(1));

But this only works if there is a conversion from int to T. For a user
defined type it would be lame to add a constructor from int just for
this purpose (and it conflict with other uses for that constructor,
like if T is a vector of some sort). It would be better to do
something like this:

accumulate(start, finish, times<T>(), number_traits<T>::one());

The other important number, of course is zero.

So I was just wondering if someone had already created such a
number_traits class.

I suppose there are other algebraic properties that would also
be nice to have access to.

I just took a quick look in Barton and Nackman... in their algebraic
structure chapter they had "setToOne()" and "setToZero()" function.

Howard Hinnant writes:
 > Not sure if this is exactly what you're looking for, but I'm currently 
 > using this in my work:
 > 
 > template <typename Size, Size sz>
 > struct number
 > {
 > 	operator Size() const {return sz;}
 > };
 > 
 > I'm using it as the default argument for a template parameter.  The 
 > client template sometimes needs a type like size_t that can take on 
 > different values, and other times the client just needs a constant.  The 
 > struct number is good for those times only a constant is needed because 
 > it is zero-sized.
 > 
 > You'll have to tell me whether this little animal solves your problem or 
 > not.
 > 
 > -Howard
 > 
 > jsiek_at_[hidden] wrote on 12/3/99 6:45 PM
 > >Just wondering if anyone has thought of doing a traits class
 > >for getting the appropriate value for zero and one given
 > >some number type.
 > >
 > >Cheers,
 > >
 > >Jeremy
 > >
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