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

From: Jan Gaspar (jano_gaspar_at_[hidden])
Date: 2005-04-20 05:54:34

Hi Fredrik,

I'm attaching the discussion during the formal review
regarding the comparison operators. But before you dip
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.

Jan

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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