Hi Frederik! I realized there is no reason to implement the comparison operators - functions std::equal() and std::lexicographical_compare() do the job. std::vector<int> v; v.push_back(1); v.push_back(2); v.push_back(3); std::deque<short> d; d.push_back(1); d.push_back(2); d.push_back(3); std::lexicographical_compare(v.begin(), v.end(), d.begin(), d.end()); std::equal(v.begin(), v.end(), d.begin()); Jan --- Fredrik Blomqvist <fredrik_blomqvist@home.se> wrote:

Jan Gaspar wrote:

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Hi Frederik,

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

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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?) I would be interested in the rationale too. Perhaps it was as "simple" as Pavel's note below.

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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. As I said, compliance with the standard is something I fully agree with, but when I (briefly..) looked into the standard it seemed like the only requirement was that containers of same type should be comparable to eachother. I don't interpret that as disallowing comparison with other instances _also_.

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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?

Well, I don't think that's totally unreasonable. The big catch in this case though, is that it would require an "infrastrucure" around an is_range<> metafunction protocol to be used with enable_if (SFINAE) code in all the operators. This is a considerable larger effort than per container lhs/rhs type flexibility.

Finally, my intention wasn't to make a big deal of this. I was mostly curios about rationales and the fact that many other components already use such a scheme, and that a recommendation for future components perhaps could be agreed upon.

Regards // Fredrik Blomqvist

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--- Fredrik Blomqvist <fredrik_blomqvist@home.se> wrote:

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Jan Gaspar wrote:

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Hi Fredrik,

I'm attaching the discussion during the formal review regarding the comparison operators. Thanks. I now remember reading some of those

posts.

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Did you reach a conclusion then? (Guess I have to dig the archives a bit...)

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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

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Subject: RE: [boost] Formal Review: Circular Buffer Date: Tue, 9 Mar 2004 09:44:34 -0800 From: "Powell, Gary" <powellg@amazon.com> To: boost@lists.boost.org

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-

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To: boost@lists.boost.org From: "Pavel Vozenilek" <pavel_vozenilek@hotmail.com>

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

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Subject: RE: [boost] Re: Formal Review: Circular Buffer Date: Tue, 9 Mar 2004 13:55:15 -0800 From: "Powell, Gary" <powellg@amazon.com> To: boost@lists.boost.org

No, but just because the standard libraries

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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

scr*wed up that

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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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