Glas List: Re: [glas] return type of operator[](size_type) for sparse vectors?

From: Toon Knapen (toon.knapen_at_[hidden])
Date: 2006-05-13 05:59:05

I have implemented a sparse-vector taking into account the remarks that 
have been made previously. I think this is a good compromise between 
performance and functionality. I uploaded the latest state of the 
documentation and the current implementation of a sparse-vector, the 
mapped_vector, can be found here 
http://glas.sourceforge.net/doc/models/container/mapped_vector.html

There is also a small test that you can find 
glas/test/sparse_vector/mapped_vector.cpp. (remember that we switched to 
subversion if you want to check it out).

toon

Russell Smiley wrote:
> I think I prefer option 3 (proxy that modifies a structural zero if
> necessary). Presumably there is some penalty for this more sophisticated
> behaviour.
> 
> If "proxy_type operator[]" is not provided how would structural zeroes
> normally be modified?
> 
> Russell.
> 
>> -----Original Message-----
> 
>> Subject: [glas] return type of operator[](size_type) for 
>> sparse vectors?
>>
>>
>> Given a sparse vector v of size 10, what would v[0] return? Should it 
>> return a reference to the element at position 0 in the sparse vector. 
>> What if that element is a structural-zero? It clearly is not as 
>> straightforward as with dense vectors.
>>
>> The options AFAICT are:
>> 1) provide no 'operator[](size_type)' to avoid confusion
>>
>> 2) return the value at the corresponding position or if the position 
>> corresponds to a structural-zero return zero. Thus in that case 
>> operator[] will not affect/change the structure and 
>> operator[] will not 
>> allow to change the value at the corresponding position.
>>
>> 3) return a proxy. If the proxy is being assigned to, the 
>> structure will 
>> be changed in case the position corresponded with a structural-zero.
>>
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-- 
Toon Knapen
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