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digitalmars.D.learn - override and package

reply "Namespace" <rswhite4 googlemail.com> writes:
Code:
----
import std.stdio;

class T1 {
protected:
	void _apply() {
		writeln("Call T1");
	}
}

class T2 : T1 {
public:
	override void _apply() {
		writeln("Call T2");
	}
}

class T3 : T1 {
protected:
	override void _apply() {
		writeln("Call T3");
	}
}

class T4 : T1 {
package:
	void _apply() { /// <-- [1]
		writeln("Call T4");
	}
}

void main()
{
	T1 t1 = new T1();
	T2 t2 = new T2();
	T3 t3 = new T3();
	T4 t4 = new T4();
	
	t1._apply();
	t2._apply();
	t3._apply();
	t4._apply();
}
----

Produce the correct output:
Call T1
Call T2
Call T3
Call T4

If I remove 'override' from T3 (or also T2) I get the correct 
deprecation message:
/d172/f194.d(19): Deprecation: overriding base class function 
without using override attribute is deprecated (f194.T3._apply 
overrides f194.T1._apply)

But if I try to write 'override' before [1], I get this error 
message:
Error: function T4._apply cannot override a non-virtual function

This seems inconsistent. I really overwrite the method, and then 
I put it in a package label.
Sep 12 2013
next sibling parent "Namespace" <rswhite4 googlemail.com> writes:
Same with private, of course.
Sep 12 2013
prev sibling parent reply Jacob Carlborg <doob me.com> writes:
On 2013-09-12 11:28, Namespace wrote:


 But if I try to write 'override' before [1], I get this error message:
 Error: function T4._apply cannot override a non-virtual function

 This seems inconsistent. I really overwrite the method, and then I put
 it in a package label.


I think the error message is pretty clear. You cannot override a 
function that isn't virtual. Private and package methods are not 
virtual. Example:

class Base
{
     void foo ()
     {
         writeln("Base.foo");
     }
}

class Sub : Base
{
     package void foo ()
     {
         writeln("Sub.foo");
     }
}

void main ()
{
     auto sub = new Sub;
     sub.foo(); // prints "Sub.foo" as expected

     Base base = sub;
     base.foo(); // prints "Base.foo"
}

-- 
/Jacob Carlborg
Sep 12 2013
next sibling parent reply "Namespace" <rswhite4 googlemail.com> writes:
On Thursday, 12 September 2013 at 11:29:22 UTC, Jacob Carlborg 
wrote:

 On 2013-09-12 11:28, Namespace wrote:


 But if I try to write 'override' before [1], I get this error 
 message:
 Error: function T4._apply cannot override a non-virtual 
 function

 This seems inconsistent. I really overwrite the method, and 
 then I put
 it in a package label.


 I think the error message is pretty clear. You cannot override 
 a function that isn't virtual. Private and package methods are 
 not virtual. Example:

 class Base
 {
     void foo ()
     {
         writeln("Base.foo");
     }
 }

 class Sub : Base
 {
     package void foo ()
     {
         writeln("Sub.foo");
     }
 }

 void main ()
 {
     auto sub = new Sub;
     sub.foo(); // prints "Sub.foo" as expected

     Base base = sub;
     base.foo(); // prints "Base.foo"
 }


Obvious. But what happend? Is the original _apply hidden?
Sep 12 2013
parent reply Jacob Carlborg <doob me.com> writes:
On 2013-09-12 13:34, Namespace wrote:


 Obvious. But what happend? Is the original _apply hidden?


If you call through an object of the same type, T4 in this case, the 
method in the base class is hidden. If you call through a base class 
reference, T1 in this case, the "_apply" method in the subclass is hidden.

-- 
/Jacob Carlborg
Sep 12 2013
parent Jacob Carlborg <doob me.com> writes:
On 2013-09-12 13:39, Jacob Carlborg wrote:


 If you call through an object of the same type, T4 in this case, the
 method in the base class is hidden. If you call through a base class
 reference, T1 in this case, the "_apply" method in the subclass is hidden.


I'm guessing it's the same as overriding non-virtual methods in C++, if 
you're familiar with that.

-- 
/Jacob Carlborg
Sep 12 2013
prev sibling parent reply "Maxim Fomin" <maxim maxim-fomin.ru> writes:
On Thursday, 12 September 2013 at 11:29:22 UTC, Jacob Carlborg
wrote:

 On 2013-09-12 11:28, Namespace wrote:


 But if I try to write 'override' before [1], I get this error 
 message:
 Error: function T4._apply cannot override a non-virtual 
 function

 This seems inconsistent. I really overwrite the method, and 
 then I put
 it in a package label.


 I think the error message is pretty clear. You cannot override 
 a function that isn't virtual. Private and package methods are 
 not virtual.


Actually error message is misleading - it complains as T1._apply
would be non-virtual function which is wrong, it is one. The
problem is not in case of overriding non-virtual function but in
attempt to override virtual function (private) by non-virtual one
(package). I think error mesage should be something like:

"Error: function T4._apply is non-virtual function and cannot
ovverride virtual function T1._apply"
Sep 12 2013
parent "Namespace" <rswhite4 googlemail.com> writes:
On Thursday, 12 September 2013 at 16:16:14 UTC, Maxim Fomin wrote:

 On Thursday, 12 September 2013 at 11:29:22 UTC, Jacob Carlborg
 wrote:

 On 2013-09-12 11:28, Namespace wrote:


 But if I try to write 'override' before [1], I get this error 
 message:
 Error: function T4._apply cannot override a non-virtual 
 function

 This seems inconsistent. I really overwrite the method, and 
 then I put
 it in a package label.


 I think the error message is pretty clear. You cannot override 
 a function that isn't virtual. Private and package methods are 
 not virtual.


 Actually error message is misleading - it complains as T1._apply
 would be non-virtual function which is wrong, it is one. The
 problem is not in case of overriding non-virtual function but in
 attempt to override virtual function (private) by non-virtual 
 one
 (package). I think error mesage should be something like:

 "Error: function T4._apply is non-virtual function and cannot
 ovverride virtual function T1._apply"


Thank you, you understand my problem. ;)
I agree, the message should be changed.
Sep 12 2013