Re: [boost] Re: Re: [circular_buffer] comparison operators

From: Jan Gaspar (jano_gaspar_at_[hidden])
Date: 2005-04-21 14:31:54

Hi Frederik,

the discussion didn't end up with a conclusion. (I
appended all the submissions regarding this comparison
operators issue.)

In my opinion, there was an idea behind the fact the
comparison operators don't work for different types at
the time the STL was being designed. Although I don't
know what idea it was. (Does anyone?) Regardless it
was good or not I'd like the circular_buffer to behave
the same way as other STL containers. I don't want to
break the contract.

On the other hand when we consider comparison between
2 circular_buffers of different types, why not to take
it one step further and allow comparison of 2
different containers. E.g.
circular_buffer<int> x  = { 1, 2, 3};
deque<short> y  = { 1, 2, 3};

x == y; // makes sense?

It doesn't matter that the containers are of different
types - it is about comparing content, isn't it?

Jan

--- Fredrik Blomqvist <fredrik_blomqvist_at_[hidden]>
wrote:
> Jan Gaspar wrote:
> > Hi Fredrik,
> >
> > I'm attaching the discussion during the formal
> review
> > regarding the comparison operators.
> Thanks. I now remember reading some of those posts.
> Did you reach a conclusion then? (Guess I have to
> dig the archives a bit...)
> 
> > into the reading, I'd like to say that my
> intension
> > was to write STL compliant container nothing less
> or
> > more and I'd like to stick with this.
> That's a goal I fully support! But to my
> understanding
> making this change wouldn't compromise compliance
> (?).
> And as mentioned, several other boost components
> already
> use this scheme, in this context most notably
> multi-index.
> 
> Regards
> // Fredrik Blomqvist
> 
> 
> > Subject: RE: [boost] Formal Review: Circular
> Buffer
> > Date: Tue, 9 Mar 2004 09:44:34 -0800
> > From: "Powell, Gary" <powellg_at_[hidden]>
> > To: boost_at_[hidden]
> >
> >
> > Shouldn't the comparison functions allow the types
> to
> > differ? I mean
> > don't they still lexigraphically compare as long
> as
> > there is a comparison
> > function F that a F b for each element exists
> >
> > circular_buffer<T, MyAlloc> x;
> > circular_buffer<S, YourAlloc> y;
> >
> > bool b = x == y; for where the operator T == S is
> > valid? And what does
> > the allocator have to do with it?
> >
> > Therefore IMO, all of the comparison functions
> should
> > change from
> >
> > template< typename T, typename Alloc>
> > bool operator F ( circular_buffer<T, Alloc> &lhs,
> >                  circular_buffer<T, Alloc> &rhs);
> >
> > to
> >
> > template< typename T1, typename Alloc1,
> >          typename T2, typename Alloc2>
> > bool operator F ( circular_buffer<T1, Alloc1>
> &lhs,
> >                  circular_buffer<T2, Alloc2>
> &rhs);
> >
> >  Yours,
> >  -Gary-
> >
> > -----------------------------------------------
> >
> >
> > To: boost_at_[hidden]
> > From: "Pavel Vozenilek"
> <pavel_vozenilek_at_[hidden]>
> >
> > Date: Tue, 9 Mar 2004 20:52:29 +0100
> > Subject: [boost] Re: Formal Review: Circular
> Buffer
> >
> >
> > Hmm, do you know a STL implementation/some
> container
> > with this feature? It may be often bug to compare
> > containers with
> > different types.
> >
> > /Pavel
> >
> >
>
-----------------------------------------------------
> >
> > Subject: RE: [boost] Re: Formal Review: Circular
> > Buffer
> > Date: Tue, 9 Mar 2004 13:55:15 -0800
> > From: "Powell, Gary" <powellg_at_[hidden]>
> > To: boost_at_[hidden]
> >
> >
> > No, but just because the standard libraries
> scr*wed up
> > is no reason to perpetuate the mistake.
> >
> > It's the rule of unexpected consequences.
> >
> > Is
> > circular_buffer<int> x  = { 1, 2, 3};
> > circular_buffer<short> y = { 1, 2 ,3};
> >
> > x == y ?? or not?
> >
> > Sure looks like it should work.
> >
> > The VTL library does it IMO correctly, allowing
> that
> > if there is an operation T1 F T2, then V1 F V2
> > compiles. Otherwise you just force the user to
> write
> > what should be library code.
> > 
> 
> 
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