Consider this code:

#include <memory>
#include <iostream>

class A
{
public:
    A(int data) : data_(data)
    { std::cout << "A(" << data_ << ")" << std::endl; }
    ~A() { std::cout << "~A()" << std::endl; }
    void a() { std::cout << data_ << std::endl; }
private:
    int data_;
};

class B
{
public:
    B(): a_(new A(13)) { std::cout << "B()" << std::endl; }
    ~B() { std::cout << "~B()" << std::endl; }
    std::function<void()> getf()
    {
        return [=]() { a_->a(); };
    }
private:
    std::shared_ptr<A> a_;
};

int main()
{
    std::function<void()> f;
    {
        B b;
        f = b.getf();
    }
    f();
    return 0;
}

Here it looks like I'm capturing a_ shared pointer by value, but when I run it on Linux (GCC 4.6.1), this is printed:

A(13)
B()
~B()
~A()
0

Obviously, 0 is wrong, because A is already destroyed. It looks like this is actually captured and is used to look up this->a_. My suspicion is confirmed when I change the capture list from [=] to [=,a_]. Then the correct output is printed and the lifetime of the objects is as expected:

A(13)
B()
~B()
13
~A()

The question:

Is this behaviour specified by the standard, implementation-defined, or undefined? Or I'm crazy and it's something entirely different?

c++ c++11
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