Re: [eigen] maxCoeff taking reference?

[David Tellenbach <david.tellenbach@xxxxxxxxxxxxx>]

Hello,

> We must make sure that this does not introduce overhead if the index(es) is not used. Perhaps with some template magic it is possible to distinguish calling
> 
>   auto [value, row,col] = A.maxCoeff();
> vs
>   auto value = A.maxCoeff();

I guess it is not possible to realise something like this without (unnecessarily) calculating the indices in the case

    auto value = A.maxCoeff();

If we allow the unnecessary index calculation this is easy to implement. Distinguishing function calls based on return types is usually really hard because return types are not used for template deduction. 

>  If that is not possible, we could of course just give one method a different name.

Another alternative would be a static function maxCoeff(A) that returns a struct (or a tuple) but this might introduce more confusion. 

Cheers,
David

> On 22. Mar 2019, at 11:54, Christoph Hertzberg <chtz@xxxxxxxxxxxxxxxxxxxxxxxx> wrote:
> 
> We must make sure that this does not introduce overhead if the index(es) is not used. Perhaps with some template magic it is possible to distinguish calling
> 
>   auto [value, row,col] = A.maxCoeff();
> vs
>   auto value = A.maxCoeff();
> 
> This would actually be very close to how Matlab "overloads" many functions. If that is not possible, we could of course just give one method a different name.
> 
> Btw: I agree on not overloading for references, as it should be obvious that these are out-parameters. O.t.o.h., with pointers there is always the ambiguity if null-pointers are allowed or not.
> 
> Christoph
> 
> On 22/03/2019 09.45, Gael Guennebaud wrote:
>> We chose pointers to emphasise they are out parameters. I would not add
>> overloads taking references but maybe a version returning everything within
>> a struct to be used with C++17 structure bindings?
>> On Thu, Mar 21, 2019 at 3:27 AM Meng Zhu <meng@xxxxxxxxxxxxx> wrote:
>>> hi, I noticed eigen maxCoeff function (
>>> https://eigen.tuxfamily.org/dox/classEigen_1_1DenseBase.html#a784e23ccbb39e7c57b70af386f94f8b5)
>>> takes pointers to return the max entry coord, and there is no overload to
>>> take reference type. is there a reason to not provide reference access?
>>> thanks.
>>> 
>>> Meng
>>> 
>>> 
>>> 
> 
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> Dr.-Ing. Christoph Hertzberg
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