Reduce with Lambdas

[Lagrang3]

In the standard library lambdas can be used for reduction operations in std::accumulate. Is there any reason why boost::mpi::all_reduce does not accept lambda functions as custom reduction operation?

Example:

#include <boost/mpi/environment.hpp>
#include <boost/mpi/communicator.hpp>
#include <boost/mpi/collectives.hpp>
namespace mpi = boost::mpi;

#include <iostream>
#include <algorithm>

int main()
{
    mpi::environment env;
    mpi::communicator world;

    {
        int a=1;
        int s = mpi::all_reduce(world,a,std::plus<int>()); // ok
        
        std::vector<int> v{1,2,3};
        int s2 = std::accumulate(v.begin(),v.end(),0,std::plus<int>()); // ok
    }
    
    {
        int a=1;
        //int s = mpi::all_reduce(world,a,[](int x,int y){return x+y;}); // error: deleted default constructor for lambdas
        
        std::vector<int> v{1,2,3};
        int s2 = std::accumulate(v.begin(),v.end(),0,[](int x,int y){return x+y;}); // ok
    }
    return 0;
}

[aminiussi]

The choice was made to remain "old school" to accommodate older compilers.

It's a choice that could be discussed tough.

[Lagrang3]

The choice was made to remain "old school" to accommodate older compilers.

That's a pity.

[aminiussi]

Yes.

---

Alain Miniussi DSI, Pôles Calcul et Genie Log. Observatoire de la Côte d'Azur Tél. : +33492003009 (Mont-Gros) +33483618544 (Sophia Antipolis) +33609650665

----- On 22 Jan 21, at 15:35, Eduardo Quintana [email protected] wrote:

The choice was made to remain "old school" to accommodate older compilers. That's a pity.

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[Lagrang3]

@aminiussi How do you test changes in the repository? There's no makefile nor anything like it. I mean is there an automatic way to get your new changes immediately on you custom boost install. Or do you just copy everything from include into boost_<version>/boost/mpi and the rest into boost_<version>/libs/mpi and then run the bootstraph.sh?

[aminiussi]

@Lagrang3 I don't do that very often but yes, I do a bootstrap.sh (either with the --prefix option or I edit the bottom of the project bjam config, as the mpi section and python section usually need some manual editing) and then I call the ./b2 install (and the b2 test, although I usually go into the ./lib/mpi/tests directory and run ../../../b2 from there).

[Lagrang3]

Can we keep this open as an improvement proposal? I would like to implement this sometime.

[aminiussi]

There is now a cmake build available, ad I copied al the bjam tests into ctest tests.

It's available on develop.