CODEWITHSUNDEEP
c++lambda
dharmatech
dharmatech

Reputation: 9527

Efficiency of nested lambdas

Here's a program where main has two lambdas defined. a calls b:

#include <iostream>

int main()
{
    auto b = []() { std::cout << "b" << std::endl; };
    auto a = [&]() { b(); };

    a();
}

Now, since b is only used by a, it can also be defined inside a:

#include <iostream>

int main()
{

    auto a = []() 
    { 
        auto b = []() { std::cout << "b" << std::endl; };

        b(); 
    };

    a();

}

My question is this: Let's suppose a is called repeatedly in a loop and so there are efficiency concerns. Can most compilers be expected to make the b-inside-a version as efficient as the b-outside-a version?

Upvotes: 0

Views: 63

Answers (1)

Lightness Races in Orbit
Lightness Races in Orbit

Reputation: 385295

It's better than that; both programs will be identical to:

#include <iostream>

int main()
{
   std::cout << "b" << std::endl;
}

Upvotes: 1

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