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struct S
{
int x;
int y;
};
std::atomic<S> asd{{1, 2}}; // what should this be? This doesn't work
Edit: Both {{1, 2}} and ({1, 2}) work in g++, neither work in clang. Is there a workaround for clang?
550
Uniform Initialization in C++ The uniform initialization is a feature that permits the usage of a consistent syntax to initialize variables and objects which are ranging from primitive type to aggregates. In other words, it introduces brace-initialization that applies braces ({}) to enclose initializer values.
If a structure variable has static storage, its members are implicitly initialized to zero of the appropriate type. If a structure variable has automatic storage, its members have no default initialization.
Direct initialization applies when initializing objects without explicit assignment. It also is also used for explicit casts, whether function-style or via static_cast and applies to Lambda closure arguments captured by value (which may be regarded as a special case of member initialization).
The initializer list is used to directly initialize data members of a class. An initializer list starts after the constructor name and its parameters.
This is clang bug 18097. Here's a long thread discussing the issue, which seems to be that clang only supports scalar types for T in atomic<T>. The C++11 standard clearly states (§29.5/1) that T can be any trivially copyable type.
Both the usages shown in the question should match this constructor
constexpr atomic(T) noexcept;
The only way I can think of working around this is to default construct atomic<S> and then use atomic::store to initialize the object.
std::atomic<S> asd;
asd.store({1,2});
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