[Dune] Default constructor in MultiLinearGeometry

[Oliver Sander]

Hi,

> of gcc, if I remember correctly). To fill an std::vector with a default
> value, you can always use
>
> const T default( your default arguments here );
> std::vector< T > myVector( size, default );
>

I tried that and it seems compile.
['Seems to' because compiling test-multilineargeometry with an additional
line std::vector< T > myVector( size, default ); made my compiler run
longer than I was willing to wait, and using all my 4GB :-) ]

Best,
Oliver

PS: Let's not discuss this in FlySpray -- I don't think anyone but us three
is interested. I retire my wish for a default constructor.  Christian,
what do you say?

> If you fill the vector linearly, you can even use
>
> std::vector< T > myVector;
> myVector.reserve( size );
> for( std::size_t i = 0; i < size; ++i )
> myVector.push_back( T( arguments for element i ) );
>
> Anyway, attached you first version of a possible patch to allow
> uninitialized MultiLinearGeometry objects. I have not tested anything,
> it just shows what this could basically look like.
>
> Best,
>
> Martin
>
>
> On 10/14/2012 11:32 AM, Christian Engwer wrote:
>> Hi Martin,
>>
>>> Apart from this, my feeling is that uninitialized objects are a very
>>> bad thing. Especially unexperienced programmers will have a hard
>>> time finding bugs caused by this. A default constructor would, of
>>> course, create an "uninitialized" geometry (in the sense that you
>>> may not use it at all).
>>
>> while I agree, that RAII is a good idea, default constructors aren't a
>> bad thing in general. For example you won't be able to store objects
>> in a std::vector, unless they have a default constructor. This is due
>> to std::vectors' memory management, which tries to avoid
>> reallocations.
>>
>> So I think a defaults constructor would be helpful. E.g. in dune-udg
>> we construct a set of entity-parts (geometries + something) between a
>> grid entity and a levelset. These entity-parts are stored (on demand,
>> for a single intersection) in an std::vector -- we are doing nearly
>> the same as return a copy on the fly, but we have to return a set and
>> thus need std::vector. A default constructor would allow us to switch
>> to MultiLinearGeometry, allowing faster computations.
>>
>> In case the corner storage does not allow default-construction, we
>> still get a useful error message.
>>
>> Cheers
>> Christian
>>
>
>
>
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