recursive lambda via reference

Question

Is this code correct?

std::function<int(int)> f = [&f](int n) -> int
{
    return n <= 1 ? 1 : n * f(n - 1);
};

int x = f(42);

Is there any potential problem with object construction before it passed as reference to lambda? Or this code absolutely correct?

Capturing f by value leads to crash in msvc2010 compiler.

Nothing wrong with the recursion but why are you capturing the lambda by reference? — JaredPar
– JaredPar, Commented Apr 6, 2012 at 16:08
@JaredPar: because if he captured it by value, he'd get a copy of the function object when the lambda was created, BEFORE f was initialized? Undefined behavior — Chris Dodd
– Chris Dodd, Commented Apr 6, 2012 at 16:16
@Xeo: I think the question is different enough to stand on its own. It's asking about whether this is legal C++11 code; that question is about the use of auto funcname rather than std::function<> funcname. — Nicol Bolas
– Nicol Bolas, Commented Apr 6, 2012 at 16:29
@Nicol: Yep, noticed that after my vote though... I deleted the comment so it wouldn't encourage other close votes. My bad. — Xeo
– Xeo, Commented Apr 6, 2012 at 16:30

Nicol Bolas · Accepted Answer · 2012-04-06 16:25:40Z

1

This should work fine, so long as you follow the rules of references to stack variables stored in lambdas. It is well-defined C++11 code.

answered Apr 6, 2012 at 16:25

Nicol Bolas

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