Re: [boost] Boost.Local Review (Nov 10, 2011 to Nov 19, 2011)

Subject: Re: [boost] Boost.Local Review (Nov 10, 2011 to Nov 19, 2011)
From: Lorenzo Caminiti (lorcaminiti_at_[hidden])
Date: 2011-11-18 18:20:40

On Fri, Nov 18, 2011 at 1:31 PM, Jeffrey Lee Hellrung, Jr.
<jeffrey.hellrung_at_[hidden]> wrote:
> On Fri, Nov 18, 2011 at 1:44 AM, Lorenzo Caminiti <lorcaminiti_at_[hidden]>wrote:
>
>> On Wed, Nov 16, 2011 at 10:24 AM, Lorenzo Caminiti
>>
> [...]
>
>> boost::function<void (int&)> counter() {
>>    int delta = 2;
>>    void BOOST_CLOSURE(int& x, bind delta) {
>>
>
> Of course, you meant "bind x" or "int x" here instead of "int& x", right?

No, I meant int& x. In this case the local function accepts one
parameter of type int& and it is closed over a copy of value of the
local variable delta. Given that none of the variables is bound by
reference (the only reference is a function parameter and not a bound
variable), such a closure can be safely returned to another scope and
executed outside the local scope (within main in this case). When main
will execute the closure, it will have to pass the one parameter x
(see inc(x) below).

>>        x += delta;
>>        std::cout << "x = " << x << std::endl;
>>    } BOOST_CLOSURE_END(increment)
>>    return increment;
>> }
>>
>> int main() {
>>    int x = 1;
>>    boost::function<void (int&)> inc = counter();
>>    inc(x); // undefined behaviour now but it should work...
>>    return 0;
>> }
>>
> [...]

Thanks.
--Lorenzo