Using brace-init to initialize a reference to std::shared_ptr

Question

I was working on a code recently and I stumbled on something unusual in GCC and Clang. Using brace-init triggers a compilation error in gcc, while a direct initialization such as &b = a works. The code below is a very simple example of that behaviour I encountered and I was wondering why GCC doesn't compile the code, since none of shared_ptr takes an initializer_list and a is a lvalue

#include <iostream>
#include <memory>

int main( )
{
    std::shared_ptr<int> a { nullptr }, &b { a };

    a = std::make_shared<int> ( 1e3 );
    std::cout << ( b ? *b : 0 ) << std::endl;

    return 0;
}

Clang 3.4 compiles this but GCC 4.8 doesn't.

Can't reproduce for gcc 4.9. Probably fixed between versions. — , Oct 04 '14 at 15:29
Might be a defect in list-initialization. Compare N3337 vs N3485. I'll try to find the defect report. — dyp, Oct 04 '14 at 15:30
Here it is: http://open-std.org/JTC1/SC22/WG21/docs/cwg_defects.html#1288 — dyp, Oct 04 '14 at 15:35

score 3 · Answer 1 · 2014-10-04T17:04:41.573

3

The CWG Defect 1288 as pointed out by @Dyp has been acknowledged and fixed for GCC 4.9.0. A workaround is to use direct initialization without list initialization:

// Note the parentheses
std::shared_ptr<int> a { nullptr }, &b ( a );

edited Oct 04 '14 at 17:04

answered Oct 04 '14 at 15:43

Using brace-init to initialize a reference to std::shared_ptr

1 Answers1