On 02/07/10 15:18, Heywood Floyd wrote:
On Jul 2, 2010, at 15:34 , Steven Schveighoffer wrote:
On Fri, 02 Jul 2010 09:32:39 -0400, Steven Schveighoffer<schvei...@yahoo.com>
wrote:
On Fri, 02 Jul 2010 09:24:20 -0400, Heywood Floyd<soul...@gmail.com> wrote:
Good day!
Consider
// - - - -
class Foo{}
auto one = new Foo();
auto two = new Foo();
writefln("one: %x two: %x",&one.classinfo,&two.classinfo);
// - - - -
For me this results in two identical memory addresses "every time".
Can I rely on this?
Can I design software based on the assumption that these addresses are always
the same?
(I'd like to be able to use the memory address as the key in an associative
array, for quick by-class
lookups.)
Use classinfo.name. The classinfo is the same memory address in the same
executable/dynamic library. If you open another D dynamic library, the
classinfo address for the same class may be different, but the name will be the
same.
Note that comparing classinfo.names will be just as fast as comparing classinfo
addresses if the names are at the same address (which will be true if the
classinfo is at the same address) because the string comparison function
short-circuits if the addresses are the same.
Duh, just realized, classinfos should use this same method to compare. Just
use the whole class info as the key, don't take the address.
-Steve
Alright thanks!
Ok, loading in code dynamically changes the addresses. Good point. Thanks!
I looked up the TypeInfo_Class-implementation and it seems to compare class
names. So that looks good. Will use the classinfos directly like you suggested.
Seems proper.
***
Hm, but still, I can't quite let go of this.
Even if the string comparer can short-circuit, it still has to go through
strings that are _not_ of the same address untill it spots a difference, as
they could potentially be equal anyway?
I noted that the classinfo.name-strings typically looks like this:
classtype.Foo
classtype.Bar
classtype.Cat
classtype.Dog
Doesn't this first "classtype."-part introduce overhead when these strings are
used as keys in an AA? The string comparer more or less always have to check the first 10
chars, which are equal for all. (I know I'm being picky here. But the whole using memory
addresses-thing came from the fear of string comparisons being suboptimal.)
/heywood
(PS. Feature-request: move the "classtype."-part of classinfo names to the end
; )
Would simply comparing slices such as classtype.name[10..$] work? Or if
you're not sure about classtype always being present every single time
(I don't know if it is), perhaps write a compile time function that
takes a string and appends a simple string checksum to the front? Then
swap classinfo.name for f(classinfo.name).
