Question

How do I assign a lambda as default argument? I would like to do this:

int foo(int i, std::function<int(int)> f = [](int x) -> int { return x / 2; })
{
    return f(i);
}

but my compiler (g++ 4.6 on Mac OS X) complains:

error: local variable 'x' may not appear in this context

EDIT:
Indeed, this was a compiler bug. The above code works fine with a recent version of gcc (4.7-20120225).

Answer 1

You could use overloading:

int foo(int i)
{
    return foo(i, [](int x) -> int { return x / 2; });
}

int foo(int i, std::function<int(int)> f)
{
    return f(i);
}