• "aelmetwaly" <aelmetwaly gawab.com> Nov 04 2004
• Ant <Ant_member pathlink.com> Nov 05 2004
• "Thomas Kuehne" <thomas-dloop kuehne.cn> Nov 05 2004
• Ant <duitoolkit yahoo.ca> Nov 05 2004
• Sjoerd van Leent <svanleent wanadoo.nl> Nov 06 2004
• "Thomas Kuehne" <thomas-dloop kuehne.cn> Nov 06 2004
• Ben Hinkle <bhinkle4 juno.com> Nov 05 2004
• Ant <duitoolkit yahoo.ca> Nov 05 2004
• "aelmetwaly" <aelmetwaly gawab.com> Nov 06 2004
• Stewart Gordon <smjg_1998 yahoo.com> Nov 08 2004

"aelmetwaly" <aelmetwaly gawab.com> writes:

Hi there,
Consider this code in C++ :

 class CMyClass
 {
  private :
  int Width;
  int Height;

  public :
  CMyClass( int W, int H ) : Width(W), Height(H) {}

  public :
  CMyClass operator+ (CMyClass c)
  {
   return CMyClass( Width + c.Width, Height + c.Height );
  }
 }

I translate this code in D like this :

 class CMyClass
 {
  private :
  int Width;
  int Height;

  public :
  this(int W, int H)
  {
   Width = W;
   Height = H;
  }

  public :
  CMyClass opAdd(CMyClass c)
  {
   // if I write it like this, the compiler cashes and give the following
error
   // error : class constructor call must be in a constructor.
   // code : return this ( Width + c.Width, Height + c.Height);

   // and if I write it like this , it gives the following error
   // error : this.Width + CMyClass.Width is not an lvalue
   // code :return new CMyClass ( Width + c.Width, Height + c.Height);

   // I have to write it like this to compile
   int w = Width + CMyClass.Width;
   int h = Height + CMyClass.Height;
   return new CMyClass(w,h);
  }

Is this wright or what?! and Why it gives these errors?

Ant <Ant_member pathlink.com> writes:

In article <cmf72p$12a0$1 digitaldaemon.com>, aelmetwaly says...
Hi there,
Consider this code in C++ :

 class CMyClass
 {
  private :
  int Width;
  int Height;


   // I have to write it like this to compile
   int w = Width + CMyClass.Width;
   int h = Height + CMyClass.Height;
   return new CMyClass(w,h);
  }


this is not an answer but another question:
aren't Width and Height private? you should not be able
to access them at all. 

what happens if they are not private (or protected)?

Ant

"Thomas Kuehne" <thomas-dloop kuehne.cn> writes:

Ant schrieb:
 In article <cmf72p$12a0$1 digitaldaemon.com>, aelmetwaly says...
Hi there,
Consider this code in C++ :

 class CMyClass
 {
  private :
  int Width;
  int Height;


   // I have to write it like this to compile
   int w = Width + CMyClass.Width;
   int h = Height + CMyClass.Height;
   return new CMyClass(w,h);
  }


 this is not an answer but another question:
 aren't Width and Height private? you should not be able
 to access them at all.

 what happens if they are not private (or protected)?


opAdd is a member function of CMyClass. Thus it has access to all private
members of
CMyClass.
Maybe you are confusing Class and Object. "private" blocks on a per class/type
level and not
on the object level.

Thomas

Ant <duitoolkit yahoo.ca> writes:

On Fri, 05 Nov 2004 23:36:44 +0100, Thomas Kuehne wrote:

 Ant schrieb:
 In article <cmf72p$12a0$1 digitaldaemon.com>, aelmetwaly says...
Hi there,
Consider this code in C++ :

 class CMyClass
 {
  private :
  int Width;
  int Height;


   // I have to write it like this to compile
   int w = Width + CMyClass.Width;
   int h = Height + CMyClass.Height;
   return new CMyClass(w,h);
  }


 this is not an answer but another question:
 aren't Width and Height private? you should not be able
 to access them at all.

 what happens if they are not private (or protected)?


 opAdd is a member function of CMyClass. Thus it has access to all private
members of
 CMyClass.
 Maybe you are confusing Class and Object. "private" blocks on a per class/type
level and not
 on the object level.
 
 Thomas


The problem I have is with c.Width: in java it's not visible.
As I said before, I don't care how it works on C++.
(I did confuse the code I cut of with the one I left in...)

I don't confuse Class and Object. ;)
D confuses class and object! :(

I use to like C++ but that was over 10 years (10? anyway, a long time) ago.

Ant

Sjoerd van Leent <svanleent wanadoo.nl> writes:

Ant wrote:
 On Fri, 05 Nov 2004 23:36:44 +0100, Thomas Kuehne wrote:
 
 
Ant schrieb:

In article <cmf72p$12a0$1 digitaldaemon.com>, aelmetwaly says...

Hi there,
Consider this code in C++ :

class CMyClass
{
 private :
 int Width;
 int Height;


  // I have to write it like this to compile
  int w = Width + CMyClass.Width;
  int h = Height + CMyClass.Height;
  return new CMyClass(w,h);
 }


this is not an answer but another question:
aren't Width and Height private? you should not be able
to access them at all.

what happens if they are not private (or protected)?


opAdd is a member function of CMyClass. Thus it has access to all private
members of
CMyClass.
Maybe you are confusing Class and Object. "private" blocks on a per class/type
level and not
on the object level.

Thomas


 
 The problem I have is with c.Width: in java it's not visible.
 As I said before, I don't care how it works on C++.
 (I did confuse the code I cut of with the one I left in...)
 
 I don't confuse Class and Object. ;)
 D confuses class and object! :(
 
 I use to like C++ but that was over 10 years (10? anyway, a long time) ago.
 
 Ant
 


Maybe I can give some enlightenment here. In Java, each protection 
attribute is on object level. That is, an instantiated object of type X 
may not access a protected member of another object of the same type (X).

In D, protection attributes are per module basis. This means that any 
object, method and template can access any protected attribute at any 
level within the same module.

For example, in D the following would work:

module x;

class X {
	private int i;

	static void usesX() {
		X x;
		int j = x.i;
	}
}

in Java, the same code would (correctly) fail, since usesX is static and 
may not access the private attribute i.

N.B. Protection levels are needed to keep other modules out. This also 
means that classes are automatically friends of themselves.

Regards,
Sjoerd

"Thomas Kuehne" <thomas-dloop kuehne.cn> writes:

Sjoerd van Leent schrieb:
 Maybe I can give some enlightenment here. In Java, each protection
 attribute is on object level. That is, an instantiated object of type X
 may not access a protected member of another object of the same type (X).

 In D, protection attributes are per module basis. This means that any
 object, method and template can access any protected attribute at any
 level within the same module.

 For example, in D the following would work:

 module x;

 class X {
 private int i;

 static void usesX() {
 X x;
 int j = x.i;
 }
 }

 in Java, the same code would (correctly) fail, since usesX is static and
 may not access the private attribute i.


code: (Java)
# class X {
#    private int i;
#
#    static void usesX() {
#        X x = new X();
#        int j = x.i;
#    }
#
#    public static void main(String args[]){
#        usesX();
#    }
#}

does compile and behaves like a D class.
The access rights are the same for D and Java. The only difference is, that all
classes in a
D module(one source file) have the same access rights as if they where inner
classes in an
Java class named like the D module.

Thomas

Ben Hinkle <bhinkle4 juno.com> writes:

aelmetwaly wrote:

 Hi there,
 Consider this code in C++ :
 
  class CMyClass
  {
   private :
   int Width;
   int Height;
 
   public :
   CMyClass( int W, int H ) : Width(W), Height(H) {}
 
   public :
   CMyClass operator+ (CMyClass c)
   {
    return CMyClass( Width + c.Width, Height + c.Height );
   }
  }
 
 I translate this code in D like this :
 
  class CMyClass
  {
   private :
   int Width;
   int Height;
 
   public :
   this(int W, int H)
   {
    Width = W;
    Height = H;
   }
 
   public :
   CMyClass opAdd(CMyClass c)
   {


    // if I write it like this, the compiler cashes and give the following
 error
    // error : class constructor call must be in a constructor.
    // code : return this ( Width + c.Width, Height + c.Height);


did the compiler really "crash"? or did it just stop compiling because of
the error? When I try it I get the error and the compiler stops without
crashing. This is what I would expect. The error message explains what is
wrong with the code.

    // and if I write it like this , it gives the following error
    // error : this.Width + CMyClass.Width is not an lvalue
    // code :return new CMyClass ( Width + c.Width, Height + c.Height);


This code works for me. Are you sure you didn't declare the constructor
arguments as inout or pointers or something?

    // I have to write it like this to compile
    int w = Width + CMyClass.Width;
    int h = Height + CMyClass.Height;
    return new CMyClass(w,h);
   }
 
 Is this wright or what?! and Why it gives these errors?

Ant <duitoolkit yahoo.ca> writes:

On Fri, 05 Nov 2004 08:37:07 +0200, aelmetwaly wrote:

 Hi there,
 Consider this code in C++ :
 
  class CMyClass
  {
   private :
   int Width;
   int Height;
 
   public :
   CMyClass( int W, int H ) : Width(W), Height(H) {}
 
   public :
   CMyClass operator+ (CMyClass c)
   {
    return CMyClass( Width + c.Width, Height + c.Height );
   }
  }
 
 I translate this code in D like this :
 
  class CMyClass
  {
   private :
   int Width;
   int Height;
 
   public :
   this(int W, int H)
   {
    Width = W;
    Height = H;
   }
 
   public :
   CMyClass opAdd(CMyClass c)
   {
    // if I write it like this, the compiler cashes and give the following
 error
    // error : class constructor call must be in a constructor.
    // code : return this ( Width + c.Width, Height + c.Height);
 
    // and if I write it like this , it gives the following error
    // error : this.Width + CMyClass.Width is not an lvalue
    // code :return new CMyClass ( Width + c.Width, Height + c.Height);
 
    // I have to write it like this to compile
    int w = Width + CMyClass.Width;
    int h = Height + CMyClass.Height;
    return new CMyClass(w,h);
   }
 
 Is this wright or what?! and Why it gives these errors?


ok, now I have D here.
1 - return this() is not valid you use "new" to create a new instance
2 - the second version compiles on linux dmd 0.105 and gives the
    expected you expected. I expected that c.Width and c.Height would
    not be visible. If I remember correctly every anything on the same
    scope is accessible indepentently of the access modifier
    (I don't like that)
3 - the final version adds to itself, ignoring the object c.
    Prefixing with the class name gives the current object (I think)
    (I don't like that)
4 - variables should start with a lower case char. 

Ant

"aelmetwaly" <aelmetwaly gawab.com> writes:

Yes ther compiler crashes after printing the error.
and the constructor declared with inout parameters


"Ant" <duitoolkit yahoo.ca> wrote in message
news:pan.2004.11.06.01.22.10.734425 yahoo.ca...
 On Fri, 05 Nov 2004 08:37:07 +0200, aelmetwaly wrote:

 Hi there,
 Consider this code in C++ :

  class CMyClass
  {
   private :
   int Width;
   int Height;

   public :
   CMyClass( int W, int H ) : Width(W), Height(H) {}

   public :
   CMyClass operator+ (CMyClass c)
   {
    return CMyClass( Width + c.Width, Height + c.Height );
   }
  }

 I translate this code in D like this :

  class CMyClass
  {
   private :
   int Width;
   int Height;

   public :
   this(int W, int H)
   {
    Width = W;
    Height = H;
   }

   public :
   CMyClass opAdd(CMyClass c)
   {
    // if I write it like this, the compiler cashes and give the




 error
    // error : class constructor call must be in a constructor.
    // code : return this ( Width + c.Width, Height + c.Height);

    // and if I write it like this , it gives the following error
    // error : this.Width + CMyClass.Width is not an lvalue
    // code :return new CMyClass ( Width + c.Width, Height + c.Height);

    // I have to write it like this to compile
    int w = Width + CMyClass.Width;
    int h = Height + CMyClass.Height;
    return new CMyClass(w,h);
   }

 Is this wright or what?! and Why it gives these errors?


 ok, now I have D here.
 1 - return this() is not valid you use "new" to create a new instance
 2 - the second version compiles on linux dmd 0.105 and gives the
     expected you expected. I expected that c.Width and c.Height would
     not be visible. If I remember correctly every anything on the same
     scope is accessible indepentently of the access modifier
     (I don't like that)
 3 - the final version adds to itself, ignoring the object c.
     Prefixing with the class name gives the current object (I think)
     (I don't like that)
 4 - variables should start with a lower case char.

 Ant

Stewart Gordon <smjg_1998 yahoo.com> writes:

aelmetwaly wrote:
 Yes ther compiler crashes after printing the error.
 and the constructor declared with inout parameters



Then why did you tell us in your original post that it isn't?

Copy and paste exists for a reason.

Stewart.