• deadalnix (8/8) Oct 07 2014 Hi all,
• bearophile (16/20) Oct 08 2014 It can't be used for GC-managed pointers. A possible usage syntax:

"deadalnix" <deadalnix gmail.com> writes:

Hi all,

There is something that is badly needed in std.butmanip : a way 
to create tagged pointers. It is doable safely by checking 
pointer alignment and allowing for n bits to be taken for various 
things.

This is something I want to do for ages (and need) but constantly 
run out of time. I think it would be useful to others as well.

Would someone champion it ?

"bearophile" <bearophileHUGS lycos.com> writes:

deadalnix:

 There is something that is badly needed in std.butmanip : a way 
 to create tagged pointers. It is doable safely by checking 
 pointer alignment and allowing for n bits to be taken for 
 various things.

It can't be used for GC-managed pointers. A possible usage syntax:

enum Tag1 { A, B, C, D }
alias TP1 = TaggedPointer!Tag1; // Uses 2 bits.
enum Tag2 { A, B }
alias TP2 = TaggedPointer!Tag2; // Uses 1 bit.
enum Tag3 { A, B, C, D, E } // 5 possibilities
alias TP3 = TaggedPointer!Tag3; // Uses 3 bits.

Alternative name "TaggedPtr".
It should verify some things statically about the given enum.

I wrote a tagged pointer struct in D1 to implement a more 
memory-succinct Trie (I think the tag was one bit, to tell apart 
nodes the terminate a word from the other nodes). But now I can't 
find the source code...

Bye,
bearophile