Replace std::function to template argument in Alg::call to avoid its …

[pmed]

…type erasure

In theory, this should improve chances for the alg inlining

[kberezovsky]

I failed to see the type erasure here. For example, the algorithm type at the line 52:

std::function<void(std::insert_iterator<DstCont>)> alg

Here we have not some void* - like type. The type is made with the information about DstCont, so the type is concrete.

[pmed]

I mean std::function uses type erasure to store various function objects inside.

In the current version lambdas supplied to the Alg::call() would be copied into a temporary std::function object for the alg argument, here for example. This may lead to a dynamic memory allocation for the lambada captured context and virtual function call on the std::function invocation. Here's some additional information: http://blog.demofox.org/2015/02/25/avoiding-the-performance-hazzards-of-stdfunction/

I suggest to use template argument alg for the Alg::call() function to pass the actual lambda object without conversion to std::function.

Actually my simple performance test doesn't show a significant improvement for this change, but at least it removes unnecessary pessimization.

[kberezovsky]

Got it. Cool. Thanks.