CODEWITHSUNDEEP
c++performancec++11lambdastdbind
tbotz
tbotz

Reputation: 227

Efficiency of std::bind vs lambda

I have searched around a bit and found many examples and discussions of cases where you would use std::bind instead of a lambda, but the burning question I have is whether or not there is any performance benefit to one over the other. I will describe my use case:

I have a generic A* I have implemented, to which I pass successor, heuristic distance, and move cost functions.

Here is an example of my heuristic function ready to be passed off for a search (in both forms):

std::function<float(const Location*, const Location*)> hdist = std::bind(&TerrainMap::straightLineDist, this, std::placeholders::_1, std::placeholders::_2);

std::function<float(const Location*, const Location*)> hdist2 = [this](const Location* a, const Location* b){
    return straightLineDist(a,b);
};

Is there any difference in the performance of these approaches? I realize the difference is probably negligible but I am curious enough to want to know.

Upvotes: 3

Views: 3312

Answers (1)

einpoklum
einpoklum

Reputation: 131626

Is there any difference in the performance of these approaches?

Perhaps, perhaps not; as commenters suggest - profile to check, or look at the assemby code you get (e.g. using the GodBolt Compiler Explorer). But you're asking the wrong question, for two main reasons:

  1. You should probably not be passing lambda's, nor bind() results, around in the part of your code that's performance-critical.
  2. You should definitely avoid invoking arbitrary functions via function pointer or std::function variables in performance-critical areas of your code (except if this can be de-virtualized and inlined by the compiler).

and one mind reason:

  1. Lambdas (and std::bind()'s) are usable, and useful, without being wrapped in std::function; this wrapper has its own performance penalty, so you would only be comparing one way of using these constructs.

Bottom line recommendation: Just use Lambdas. They're cleaner, easier to understand, cheaper to compile, and more flexible syntactically. So don't worry and be happy :-) . And in performance-critical code, either use Lambda's without std::function, or don't use any of the two.

Upvotes: 2

Related Questions