[D-runtime] dup attributes?

[Steve Schveighoffer]

Well, no, not exactly like that.

The issue is, if you have two void[]'s, and each one has flags associated with 
them, the flags of the existing blocks are disregarded.  The flags of the void[] 
type are used instead.

So something like this:

int[] x = new int[20];

void[] y = x; // y is still the same block, so the NO_SCAN bit is set

y ~= y; // appending preserves bit, so NO_SCAN bit remains set

y = y ~ y; // concatenation ignores the bits of the arguments, so the type is 
used to determine bits.  y now has the NO_SCAN bit cleared.

y = x; // reset

y = y.dup; // dup ignores current flags, the type is used instead.

-Steve



----- Original Message ----
> From: Sean Kelly <sean at invisibleduck.org>
> To: D's runtime library developers list <d-runtime at puremagic.com>
> Sent: Thu, August 5, 2010 7:15:19 PM
> Subject: Re: [D-runtime] dup attributes?
> 
> Concatenation doesn't preserve bit flags?  Like if I do this:
> 
> mystr  ~= "a" ~ "b";
> 
> You're saying that it's possible for the bits set on mystr  to be lost?
> 
> On Aug 4, 2010, at 10:19 AM, Steve Schveighoffer  wrote:
> 
> > One more thing -- concatenation suffers from the same  problem.  This one 
>might 
>
> > be much harder to swallow since you may  have to do N flag lookups.
> > 
> > -Steve
> > 
> > 
> > 
> > ----- Original Message ----
> >> From: Steve Schveighoffer  <schveiguy at yahoo.com>
> >> To:  d-runtime <d-runtime at puremagic.com>
> >>  Sent: Wed, August 4, 2010 8:32:38 AM
> >> Subject: [D-runtime] dup  attributes?
> >> 
> >> Currently, in the array runtime code, all  appends and length settings copy 
>the 
>
> > 
> >> BlkAttr attributes  from the existing block to the new block.  This is  
> >>  important 
> >> 
> >> if you set block attributes other than the  default, or you are  appending 
>to a 
>
> > 
> >> block which is  currently typed differently than what it was  when 
>allocated.
> >> 
> >> However, the one function which does *not* do this is   dup.  dup uses the 
> >> typeinfo to determine the block  attributes,  including the NO_SCAN flag.
> >> 
> >> I think  it should copy the attributes like  all the other functions do.  
> >> However, 
> >> 
> >> there is one caveat to   this.  Currently dup doesn't look up the block 
> >> attributes 
> >> 
> >> of the  existing data, because it doesn't have  to.  So changing dup to copy 
>the 
>
> >> 
> >> attributes would  slow down dup a bit because in addition to allocating a 
>new 
>
> >> block,  it must look up the flags for the old block.
> >> 
> >> What do  you guys  think?
> >> 
> >> -Steve
> >> 
> >> 
> >> 
> >> 
> >>  _______________________________________________
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> >> D-runtime at puremagic.com
> >>  http://lists.puremagic.com/mailman/listinfo/d-runtime
> >> 
> > 
> > 
> > 
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