digitalmars.D.bugs - [Issue 3939] New: Built-in __vptr attribute for classes too
- d-bugmail puremagic.com (36/36) Mar 12 2010 http://d.puremagic.com/issues/show_bug.cgi?id=3939
- d-bugmail puremagic.com (22/22) Oct 24 2010 http://d.puremagic.com/issues/show_bug.cgi?id=3939
http://d.puremagic.com/issues/show_bug.cgi?id=3939 Summary: Built-in __vptr attribute for classes too Product: D Version: 2.041 Platform: All OS/Version: All Status: NEW Severity: enhancement Priority: P2 Component: DMD AssignedTo: nobody puremagic.com ReportedBy: bearophile_hugs eml.cc The attribute __vptr of object instances can be useful in some special situations. To compare the __vptr of an object instance to the __vptr of a class you first need to find the __vptr of a class. You can do it with code similar to: class Foo { __gshared static immutable(immutable(void)*) __vptr; static this() { scope auto aux = new typeof(this); __vptr = aux.__vptr; } //... } void main() {} But this is not handy (even if a class mixin can help). So a built-in __vptr attribute can be added to classes too. Possible disadvantages: the need for __vptr is rare. ------------- Note: there are other ways to implement virtual functions, like using a dispatch tree, so the D docs can say that __vptr can be absent in D compilers that don't use a virtual table or in other situations. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Mar 12 2010
http://d.puremagic.com/issues/show_bug.cgi?id=3939 Currently this seems the most efficient way to have a static class attribute that contains a __vptr (here converted to a size_t and named classId): class Foo { static immutable size_t classId; static this() { classId = *(cast(size_t*)(typeid(Foo).init.ptr)); } } void main() { assert(cast(size_t)((new Foo).__vptr) == Foo.classId); } With it DMD 2.049 generates a very light static constructor: _D4test3Foo12_staticCtor1FZv comdat mov EAX,_D4test3Foo7__ClassZ[0Ch] mov ECX,[EAX] mov _D4test3Foo7classIdyk,ECX ret -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Oct 24 2010