IsValueType template? std.traits.hasAliasing?

[Bill Baxter]

On Wed, Jan 28, 2009 at 11:11 AM, dsimcha <dsimcha at yahoo.com> wrote:
> == Quote from dsimcha (dsimcha at yahoo.com)'s article
>> == Quote from Bill Baxter (wbaxter at gmail.com)'s article
>> > Does anyone have a good template for checking if a struct is
>> > semantically a pure value type or not?
>> > I found "hasAliasing" in D2 which is close, but it seems to report
>> > true even for static arrays.
>> > struct X { float[3] vals; }
>> > pragma(msg, hasAliasing!(X)?"true":"false"); --> true
>> > Maybe that's just a bug in hasAliasing?
>> > What I want to know is if     X=Y will give me an X that is
>> > independent of Y.  I think that is the same question hasAliasing is
>> > trying to answer.  If so then it's a bug.
>> > --bb
>> Here's a really ugly, brute force hack that does what you need:
>> http://dsource.org/projects/dstats/browser/trunk/alloc.d
>> I actually needed it in dstats to support newVoid(), which is a speed hack to
>> allocate arrays w/o initializing the contents, to tell the GC whether to scan for
>> pointers.  Actually, on looking at it again, it should probably be changed to make
>> function pointers and delegates return false.
>> Not sure if this is what you were looking for.  By semantically a pure value type,
>> do you mean that immutable reference data should or sould not be included?
>
> Forgot to mention:  It's isReferenceType, about 1/3 of the way down.
>

Got it.

I see looking there that my one line fix to hasAliasing above won't
work.  It ignores the possibility that the T in a static array T[3]
itself may have references.

--bb