CODEWITHSUNDEEP
c++lambdareference
user8024280
user8024280

Reputation:

Passing a reference to lambda by reference

Is there any difference between f1 and f2?

void foo(const std::string& test){

    auto f1 = [&test](){
        std::cout << test << std::endl;
    };

    f1();

    auto f2 = [test](){
        std::cout << test << std::endl;
    };

    f2();
}

int main()
{
    std::string x = "x";
    foo(x);
}

It looks like in both cases, the type of the test variable inside of the lambda will be std::string const&, but is it really the same?

Upvotes: 4

Views: 1615

Answers (1)

eerorika
eerorika

Reputation: 238321

Is there any difference between f1 and f2?

Yes.

but is it realy the same?

No. f2 captures a std::string const.

Type deduction of lambda captures works the same as auto declarations:

[&test](){}              // a reference
[ test](){}              // an object

auto        &var = test; // a reference
auto         var = test; // an object

std::string &var = test; // a reference
std::string  var = test; // an object

template<class T> void foo1(T& var);
template<class T> void foo2(T  var);
foo1(test);              // a reference
foo2(test);              // an object

Upvotes: 8

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