Meaning of double bracket “[[foo()]] type name;” syntax in c++?

Question

In this article about avoiding False Sharing, the following code snipped for alignment is presented:

// C++ (using C++0x alignment syntax)
template

        

Answer 1

That is the attribute specifier syntax. It was introduced as a unified syntax to access what were formerly compiler-specific extensions (now some are standardized).

In this case the code is telling the compiler to align data to CACHE_LINE_SIZE bytes.