C++ class specifier alignas option via template

Question

Can C++ template parameters be used to control specifiers on the class itself to minimize some code duplication?

For example: I have a class that I'd like to use both in a concurrent context (and container) with the alignas specifier, and also in a single-threaded context without the alignas specifier. The size of the class is small (20B) -- less than a cache line. I do need to copy between the two classes. Right now I have duplicated code for the two definitions of the two classes which are the same, mostly, other than the said specifier. Can templates or otherwise allow a single definition, one with alignas and one without?

Will you be using the class with and without the `alignas` specifier in a single project? — NathanOliver, Nov 23 '20 at 17:01
You say that you need to be able to copy between two versions of the class. But keep in mind that templates are not inheritance. So they are treated as a completely different class once the compilation actually starts. — v010dya, Nov 23 '20 at 17:05
@Eugene to prevent false-sharing in a producer-consumer situation — Kulluk007, Nov 23 '20 at 18:58

score 3 · Accepted Answer · answered Nov 23 '20 at 17:10

3

You can do it like this:

template <size_t alignment = 0>
class alignas(alignment) C {
    // ...
};

Now C<> will have the default alignment for its definition (since alignas(0) is ignored) while you could use e.g. C<16> to force an alignment of 16.

answered Nov 23 '20 at 17:10

Brian Bi

111,498
10
176
312

C++ class specifier alignas option via template

1 Answers1