• via Digitalmars-d-bugs (40/40) Sep 10 2016 https://issues.dlang.org/show_bug.cgi?id=16485

via Digitalmars-d-bugs <digitalmars-d-bugs puremagic.com> writes:

https://issues.dlang.org/show_bug.cgi?id=16485

          Issue ID: 16485
           Summary: Add trait for determining whether a member variable is
                    static or not
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P1
         Component: phobos
          Assignee: nobody puremagic.com
          Reporter: issues.dlang jmdavisProg.com

We should probably have a trait in std.traits either for checking whether a
member variable is static or for checking that it's not static. It's something
that seems to have come up several times recently in D.Learn and stackoverflow.
I don't know that this is the best implementation, since it was just quickly
thrown together, but this would be one possible implementation:


    template isStaticMember(T, string memberName)
        if(__traits(hasMember, T, memberName))
    {
        mixin("alias member = " ~ T.stringof ~ "." ~ memberName ~ ";");
        enum isStaticMember = !__traits(compiles, member.offsetof);
    }

    class C
    {
        int foo;
        static int bar;
    }

    void main()
    {
        static assert(!isStaticMember!(C, "foo"));
        static assert(isStaticMember!(C, "bar"));
    }

But the fact that it's the offsetof property that is the key is definitely
non-obvious and not something that it's reasonable to expect that your average
programmer is going to think of, so putting something like this in std.traits
would definitely be beneficial.

--