Add function_ref

[nsavoire]

Based on PR #336

Add https://github.com/zhihaoy/nontype_functional as third party, this provides a function_ref implementation (non-owning cheap alternative to std::function).

[pr-commenter]

Benchmark results for collatz

Parameters

	Baseline	Candidate
config	baseline	candidate
profiler-version	ddprof 0.15.0+99326392.22228515	ddprof 0.15.0+66f9c5b0.22279541

Summary

Found 0 performance improvements and 0 performance regressions! Performance is the same for 1 metrics, 0 unstable metrics.

See unchanged results

scenario	Δ mean execution_time
scenario:ddprof -S bench-collatz --preset cpu_only collatz_runner.sh	unsure [-50.198ms; -1.137ms] or [-1.289%; -0.029%]

[pr-commenter]

Benchmark results for BadBoggleSolver_run

Parameters

	Baseline	Candidate
config	baseline	candidate
profiler-version	ddprof 0.15.0+99326392.22228515	ddprof 0.15.0+66f9c5b0.22279541

Summary

Found 0 performance improvements and 0 performance regressions! Performance is the same for 1 metrics, 0 unstable metrics.

See unchanged results

scenario	Δ mean execution_time
scenario:ddprof -S bench-bad-boggle-solver BadBoggleSolver_run work 1000	same

[r1viollet]

Where do we need this ?

[nsavoire]

Where do we need this ?

In an earlier version of my PR to reduce allocation event size, I was passing a callback to save_context to reserve size in ring buffer. function_ref allowed to pass a capturing lambda without the extra cost associated to std::function.
Since I changed my implementation, I do not need this anymore, I changed the PR status to draft.

[r1viollet]

Where do we need this ?

In an earlier version of my PR to reduce allocation event size, I was passing a callback to save_context to reserve size in ring buffer. function_ref allowed to pass a capturing lambda without the extra cost associated to std::function. Since I changed my implementation, I do not need this anymore, I changed the PR status to draft.

Thanks for leaving as draft. I was actually considering std::functions recently and was not sure of the cost.