• Namespace (2/2) Aug 11 2012 This code works fine but it shouldn't, or?
• Adam D. Ruppe (17/18) Aug 11 2012 The reason is the print method is private, which means it is also
• David Nadlinger (4/6) Aug 11 2012 You don't actually dereference ›this‹ in print(), so the null
• Marco Leise (8/11) Aug 11 2012 That's fine. There is no check for null at every possible occasion, like...

"Namespace" <rswhite4 googlemail.com> writes:

This code works fine but it shouldn't, or?

http://dpaste.dzfl.pl/b9027fff

"Adam D. Ruppe" <destructionator gmail.com> writes:

On Saturday, 11 August 2012 at 22:23:12 UTC, Namespace wrote:
 This code works fine but it shouldn't, or?


The reason is the print method is private, which means it is also 
automatically final and doesn't access any member variables. 
Since it doesn't access members, it doesn't actually try to use 
the object and thus works ok.

(You can access private methods as long as you are still in the 
same module, so this is by design too.)

It being final is important because it means it is just a regular 
function - it doesn't need to access the object's virtual 
function table either.


If it was a public final method, it would say "AssertEerror: null 
this", but since it is private I think that check is 
intentionally left out.



But what you have here is everything working right, but the rule 
might seem weird... it's just because you aren't actually 
accessing the object, so the fact that it is null never comes 
into play.

"David Nadlinger" <see klickverbot.at> writes:

On Saturday, 11 August 2012 at 22:23:12 UTC, Namespace wrote:
 This code works fine but it shouldn't, or?

 http://dpaste.dzfl.pl/b9027fff

You don't actually dereference ›this‹ in print(), so the null 
value in the implicit this parameter doesn't matter.

David

Marco Leise <Marco.Leise gmx.de> writes:

Am Sun, 12 Aug 2012 00:23:10 +0200
schrieb "Namespace" <rswhite4 googlemail.com>:

 This code works fine but it shouldn't, or?
 
 http://dpaste.dzfl.pl/b9027fff

That's fine. There is no check for null at every possible occasion, like I
think in Java. The operating system will catch any actual null dereference
though, by notifying you of an invalid memory access.
So in other words, D uses the fast approach.

Cases where your print will not work is, when print() is a virtual method of
that class (one that can be overridden). That would need to actually
dereference the object to take a look into the virtual method table.
'private' and 'final' methods (or methods of a 'final class') are not virtual.

-- 
Marco