function returning nullptr with no return

Question

On Overload Jouranl for this month I found an article about how to design Observer pattern with C++11. You'll find it here. The reading is interesting but I found a piece of code using std::atomic I don't really understand.

What is the meaning of function next below? It doesn't even seem a function declaration (no return keyword). I am using g++ 4.7.2

#include <iostream>
#include <cstddef>
#include <atomic>

struct ListItem {
 ListItem() {}
 ...
 atomic<ListItem*> next{nullptr};
 ~ListItem() { delete next.load(); }
 };

score 4 · Accepted Answer · edited May 23 '17 at 11:57

4

That isn't a function but a member declaration with a non-static data member initializer.

atomic<ListItem*> next{nullptr};

In a constructor that does not initialize next, next will automatically be initialized with nullptr. The initialization is done via list-initialization which was introduced in C++11 (together with non-static data member initializers - the latter partly depends on the former).

GCC 4.7.x should support this.

edited May 23 '17 at 11:57

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answered Dec 09 '14 at 17:22

Columbo

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For OP's benefit: Specifically, it uses the new C++11 *universal initialization* syntax, which uses braces (`{}`) instead of parens. – cdhowie Dec 09 '14 at 17:22
@cdhowie It cannot use parentheses anyway. – Columbo Dec 09 '14 at 17:23
I know, but that's not the point. OP may not be familiar with this new C++11 syntax, so I'm putting a name to it. – cdhowie Dec 09 '14 at 17:23
@cdhowie I know that it's not the point. :o) (I'll adjust the answer in a second) – Columbo Dec 09 '14 at 17:24
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@cdhowie: The name is *list-initialization*, not "universal initialization". – Mike Seymour Dec 09 '14 at 17:30

function returning nullptr with no return

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