• JN (19/19) Dec 28 2019 import std.stdio;
• Mike Parker (7/26) Dec 28 2019 Expected. Member variables do not override base class variables.
• Johan Engelen (8/40) Dec 28 2019 What Mike is saying is that `Base` has one `b` member variable,
• JN (5/12) Dec 28 2019 That makes sense. I think the compiler/linter should be warning

JN <666total wp.pl> writes:

import std.stdio;

class Base
{
     bool b = true;
}

class Derived : Base
{
     bool b = false;
}

void main()
{
// 1
     Base b = new Derived();
     writeln(b.b); // true
// 2
     Derived d = new Derived();
     writeln(d.b); // false
}


Expected behavior or bug? 1) seems like a bug to me.

Mike Parker <aldacron gmail.com> writes:

On Saturday, 28 December 2019 at 20:22:51 UTC, JN wrote:
 import std.stdio;

 class Base
 {
     bool b = true;
 }

 class Derived : Base
 {
     bool b = false;
 }

 void main()
 {
 // 1
     Base b = new Derived();
     writeln(b.b); // true
 // 2
     Derived d = new Derived();
     writeln(d.b); // false
 }


 Expected behavior or bug? 1) seems like a bug to me.

Expected. Member variables do not override base class variables. 
b is declared as Base, so it knows nothing about Derived’s member 
variable even though you instantiated it with an instance of 
Derived. There’s no vtable for variables. If you want it to print 
false, then you either have to cast b to Derived or provide a 
getter function in Base that Derived can override.

Johan Engelen <j j.nl> writes:

On Saturday, 28 December 2019 at 20:47:38 UTC, Mike Parker wrote:
 On Saturday, 28 December 2019 at 20:22:51 UTC, JN wrote:
 import std.stdio;

 class Base
 {
     bool b = true;
 }

 class Derived : Base
 {
     bool b = false;
 }

 void main()
 {
 // 1
     Base b = new Derived();
     writeln(b.b); // true
 // 2
     Derived d = new Derived();
     writeln(d.b); // false
 }


 Expected behavior or bug? 1) seems like a bug to me.

 Expected. Member variables do not override base class 
 variables. b is declared as Base, so it knows nothing about 
 Derived’s member variable even though you instantiated it with 
 an instance of Derived. There’s no vtable for variables. If you 
 want it to print false, then you either have to cast b to 
 Derived or provide a getter function in Base that Derived can 
 override.

What Mike is saying is that `Base` has one `b` member variable, 
but `Derived` has two (!).

```
writeln(d.b); // false
writeln(d.Base.b); // true (the `b` member inherited from Base)
```

-Johan

JN <666total wp.pl> writes:

On Saturday, 28 December 2019 at 22:12:38 UTC, Johan Engelen 
wrote:
 What Mike is saying is that `Base` has one `b` member variable, 
 but `Derived` has two (!).

 ```
 writeln(d.b); // false
 writeln(d.Base.b); // true (the `b` member inherited from Base)
 ```

 -Johan

That makes sense. I think the compiler/linter should be warning 
against such cases though, because it's easy to make mistakes 
this way.