• Etienne Cimon (13/13) Oct 23 2014 I'm trying to figure out the size difference between a final class and a...
• bearophile (6/7) Oct 23 2014 In D all class instances contain a pointer to the class and a
• Etienne Cimon (3/8) Oct 23 2014 So what's the point of making a class or methods final? Does it only
• bearophile (5/6) Oct 23 2014 It forbids subclassing. And final methods are not virtual, so
• Simen Kjaeraas (16/27) Oct 23 2014 Like bearophile said the vtable is required for virtual methods.

Etienne Cimon <etcimon gmail.com> writes:

I'm trying to figure out the size difference between a final class and a 
class (which carries a vtable pointer).

import std.stdio;

class A { void print(){} }

final class B { void print(){} }

void main(){
         writeln(__traits(classInstanceSize, A));
         writeln(__traits(classInstanceSize, B));
}


Returns:
8
8

I'm not sure, why does a final class carry a vtable pointer?

"bearophile" <bearophileHUGS lycos.com> writes:

Etienne Cimon:

 I'm not sure, why does a final class carry a vtable pointer?

In D all class instances contain a pointer to the class and a 
monitor pointer. The table is used for run-time reflection, and 
for standard virtual methods like toString, etc.

Bye,
bearophile

Etienne Cimon <etcimon gmail.com> writes:

On 2014-10-23 20:12, bearophile wrote:
 In D all class instances contain a pointer to the class and a monitor
 pointer. The table is used for run-time reflection, and for standard
 virtual methods like toString, etc.

 Bye,
 bearophile

So what's the point of making a class or methods final? Does it only 
free some space and allow inline to take place?

"bearophile" <bearophileHUGS lycos.com> writes:

Etienne Cimon:

 So what's the point of making a class or methods final?

It forbids subclassing. And final methods are not virtual, so 
they can be inlined.

Bye,
bearophile

"Simen Kjaeraas" <simen.kjaras gmail.com> writes:

On Friday, 24 October 2014 at 00:21:52 UTC, Etienne Cimon wrote:
 On 2014-10-23 20:12, bearophile wrote:
 In D all class instances contain a pointer to the class and a 
 monitor
 pointer. The table is used for run-time reflection, and for 
 standard
 virtual methods like toString, etc.

 Bye,
 bearophile

 So what's the point of making a class or methods final? Does it 
 only free some space and allow inline to take place?

Like bearophile said the vtable is required for virtual methods. 
Consider this code:

import std.stdio : writeln;

class A { void foo() {writeln("A");} }
final class B : A { override void foo() {writeln("B");} }

void main() {
     A a = new B();
     a.foo();
}

In order for the call to foo to run the correct version of foo, B 
needs to have a vtable. Since all classes in D implicitly inherit 
from Object, which has some virtual methods, all classes need to 
have a vtable.

--
   Simen