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digitalmars.D.learn - *final* class member (D2)

reply Denton Cockburn <diboss hotmail.com> writes:
How do I do this?  I'm trying to create a class member here that needs to
be initialized in the constructor, but cannot be changed later.

class A
{
   (const doesn't work) real delegate() dg; // this is that
   function;

   this(real delegate() dg) { this.dg = dg; }
}

class B
{
   real foo() { return 3.5; }
}

class C
{
   real foo() { return 4.5; }
}

void main()
{
   auto b = new B;
   auto a = new A(&b.foo);
   auto c = new C;
   a.fitness = &c.foo; // I want this to be an error
}
Feb 13 2008
next sibling parent reply Denton Cockburn <diboss hotmail.com> writes:
On Wed, 13 Feb 2008 10:59:26 -0500, Denton Cockburn wrote:


 How do I do this?  I'm trying to create a class member here that needs to
 be initialized in the constructor, but cannot be changed later.
 
 class A
 {
    (const doesn't work) real delegate() dg; // this is that
    function;
 
    this(real delegate() dg) { this.dg = dg; }
 }
 
 class B
 {
    real foo() { return 3.5; }
 }
 
 class C
 {
    real foo() { return 4.5; }
 }
 
 void main()
 {
    auto b = new B;
    auto a = new A(&b.foo);
    auto c = new C;
    a.fitness = &c.foo; // I want this to be an error
 }



formatting issues:

(const doesn't work) real delegate() dg; // this is that
   function;

should be:

(const doesn't work) real delegate() dg; // this is that function
Feb 13 2008
next sibling parent reply Robert Fraser <fraserofthenight gmail.com> writes:
Denton Cockburn wrote:

 On Wed, 13 Feb 2008 10:59:26 -0500, Denton Cockburn wrote:
 

 How do I do this?  I'm trying to create a class member here that needs to
 be initialized in the constructor, but cannot be changed later.

 class A
 {
    (const doesn't work) real delegate() dg; // this is that
    function;

    this(real delegate() dg) { this.dg = dg; }
 }

 class B
 {
    real foo() { return 3.5; }
 }

 class C
 {
    real foo() { return 4.5; }
 }

 void main()
 {
    auto b = new B;
    auto a = new A(&b.foo);
    auto c = new C;
    a.fitness = &c.foo; // I want this to be an error
 }



 formatting issues:
 
 (const doesn't work) real delegate() dg; // this is that
    function;
 
 should be:
 
 (const doesn't work) real delegate() dg; // this is that function
 



Use "final" :-)
Feb 13 2008
parent reply Robert Fraser <fraserofthenight gmail.com> writes:
Robert Fraser wrote:

 Denton Cockburn wrote:

 On Wed, 13 Feb 2008 10:59:26 -0500, Denton Cockburn wrote:


 How do I do this?  I'm trying to create a class member here that 
 needs to
 be initialized in the constructor, but cannot be changed later.

 class A
 {
    (const doesn't work) real delegate() dg; // this is that
    function;

    this(real delegate() dg) { this.dg = dg; }
 }

 class B
 {
    real foo() { return 3.5; }
 }

 class C
 {
    real foo() { return 4.5; }
 }

 void main()
 {
    auto b = new B;
    auto a = new A(&b.foo);
    auto c = new C;
    a.fitness = &c.foo; // I want this to be an error
 }



 formatting issues:

 (const doesn't work) real delegate() dg; // this is that
    function;

 should be:

 (const doesn't work) real delegate() dg; // this is that function



 Use "final" :-)



Oops, I thought you meant member function. AFAIK, there's no way to do 
that for a member variable.
Feb 13 2008
parent reply Jason House <jason.james.house gmail.com> writes:
Robert Fraser Wrote:


 Robert Fraser wrote:

 Denton Cockburn wrote:

 On Wed, 13 Feb 2008 10:59:26 -0500, Denton Cockburn wrote:


 How do I do this?  I'm trying to create a class member here that 
 needs to
 be initialized in the constructor, but cannot be changed later.

 class A
 {
    (const doesn't work) real delegate() dg; // this is that
    function;

    this(real delegate() dg) { this.dg = dg; }
 }

 class B
 {
    real foo() { return 3.5; }
 }

 class C
 {
    real foo() { return 4.5; }
 }

 void main()
 {
    auto b = new B;
    auto a = new A(&b.foo);
    auto c = new C;
    a.fitness = &c.foo; // I want this to be an error
 }



 formatting issues:

 (const doesn't work) real delegate() dg; // this is that
    function;

 should be:

 (const doesn't work) real delegate() dg; // this is that function



 Use "final" :-)



 Oops, I thought you meant member function. AFAIK, there's no way to do 
 that for a member variable.



I thought member variables with a const storage class could be initialized in
the constructor.  I thought it was possible to do stuff like:
class X{
  const int a;
  this(int b){ a = b; }
}

Am I wrong about that?  If not, why can't this apply to delegates?  Could it be
confusion about return type verses const storage class?  If that's the problem,
enclosing with const{} could solve the problem...
Feb 13 2008
parent Denton Cockburn <diboss hotmail.com> writes:
On Wed, 13 Feb 2008 15:50:39 -0500, Jason House wrote:


 Robert Fraser Wrote:
 

 Robert Fraser wrote:

 Denton Cockburn wrote:

 On Wed, 13 Feb 2008 10:59:26 -0500, Denton Cockburn wrote:


 How do I do this?  I'm trying to create a class member here that 
 needs to
 be initialized in the constructor, but cannot be changed later.

 class A
 {
    (const doesn't work) real delegate() dg; // this is that
    function;

    this(real delegate() dg) { this.dg = dg; }
 }

 class B
 {
    real foo() { return 3.5; }
 }

 class C
 {
    real foo() { return 4.5; }
 }

 void main()
 {
    auto b = new B;
    auto a = new A(&b.foo);
    auto c = new C;
    a.fitness = &c.foo; // I want this to be an error
 }



 formatting issues:

 (const doesn't work) real delegate() dg; // this is that
    function;

 should be:

 (const doesn't work) real delegate() dg; // this is that function



 Use "final" :-)



 Oops, I thought you meant member function. AFAIK, there's no way to do 
 that for a member variable.



 I thought member variables with a const storage class could be initialized in
the constructor.  I thought it was possible to do stuff like:
 class X{
   const int a;
   this(int b){ a = b; }
 }
 
 Am I wrong about that?  If not, why can't this apply to delegates?  Could it
be confusion about return type verses const storage class?  If that's the
problem, enclosing with const{} could solve the problem...



I would have thought I would've been able to use const as well.
I got an error when I did it.

the const applies as: const(real delegate()) dg - but it doesn't affect
the ability to reassign the variable.  It gave errors when I tried to
assign it to the delegate parameter (&b.foo) because &b.foo was a real
delegate(), and not a const(real delegate()).
Feb 13 2008
prev sibling parent "Simen Kjaeraas" <simen.kjaras gmail.com> writes:
On Wed, 13 Feb 2008 17:07:47 +0100, Denton Cockburn <diboss hotmail.com>=
  =

wrote:


 On Wed, 13 Feb 2008 10:59:26 -0500, Denton Cockburn wrote:


 How do I do this?  I'm trying to create a class member here that need=








 to
 be initialized in the constructor, but cannot be changed later.

 class A
 {
    (const doesn't work) real delegate() dg; // this is that
    function;

    this(real delegate() dg) { this.dg =3D dg; }
 }

 class B
 {
    real foo() { return 3.5; }
 }

 class C
 {
    real foo() { return 4.5; }
 }

 void main()
 {
    auto b =3D new B;
    auto a =3D new A(&b.foo);
    auto c =3D new C;
    a.fitness =3D &c.foo; // I want this to be an error
 }



 formatting issues:

 (const doesn't work) real delegate() dg; // this is that
    function;

 should be:

 (const doesn't work) real delegate() dg; // this is that function




You could make the delegate private, and use a function to call it.

class A
{
private:
	real delegate() m_dg;
public:
	real dg()
	{
		return m_dg();
	}
	this(real delegate() _dg)
	{
		m_dg =3D _dg;
	}
}

Of course, private in D only means module-private, so whoever makes  =

changes to the module might still break things, but for anyone just  =

importing it, the problem should be gone.
Feb 13 2008
prev sibling next sibling parent reply "Steven Schveighoffer" <schveiguy yahoo.com> writes:
"Denton Cockburn" wrote

 How do I do this?  I'm trying to create a class member here that needs to
 be initialized in the constructor, but cannot be changed later.

 class A
 {
   (const doesn't work) real delegate() dg; // this is that
   function;

   this(real delegate() dg) { this.dg = dg; }
 }

 class B
 {
   real foo() { return 3.5; }
 }

 class C
 {
   real foo() { return 4.5; }
 }

 void main()
 {
   auto b = new B;
   auto a = new A(&b.foo);
   auto c = new C;
   a.fitness = &c.foo; // I want this to be an error
 }



um... did you try encapsulation?

class A
{
   private real delegate() _dg;

   public real dg()
   {
      return _dg();
   }

   this(real delegate() dg) { this._dg = dg; }
}

-Steve
Feb 13 2008
parent reply Denton Cockburn <diboss hotmail.com> writes:
On Wed, 13 Feb 2008 14:33:33 -0500, Steven Schveighoffer wrote:


 "Denton Cockburn" wrote

 How do I do this?  I'm trying to create a class member here that needs to
 be initialized in the constructor, but cannot be changed later.

 class A
 {
   (const doesn't work) real delegate() dg; // this is that
   function;

   this(real delegate() dg) { this.dg = dg; }
 }

 class B
 {
   real foo() { return 3.5; }
 }

 class C
 {
   real foo() { return 4.5; }
 }

 void main()
 {
   auto b = new B;
   auto a = new A(&b.foo);
   auto c = new C;
   a.fitness = &c.foo; // I want this to be an error
 }



 um... did you try encapsulation?
 
 class A
 {
    private real delegate() _dg;
 
    public real dg()
    {
       return _dg();
    }
 
    this(real delegate() dg) { this._dg = dg; }
 }
 
 -Steve



This was the workaround I used as well.
I don't like it because of the extra level of indirection (I end up
calling 2 functions instead of 1).  I don't consider this very efficient
or convenient.
Feb 13 2008
parent reply "Neil Vice" <sardonicpresence gmail.com> writes:
"Denton Cockburn" <diboss hotmail.com> wrote in message 
news:pan.2008.02.13.22.55.38.263151 hotmail.com...

 On Wed, 13 Feb 2008 14:33:33 -0500, Steven Schveighoffer wrote:


 "Denton Cockburn" wrote

 How do I do this?  I'm trying to create a class member here that needs 
 to
 be initialized in the constructor, but cannot be changed later.

 class A
 {
   (const doesn't work) real delegate() dg; // this is that
   function;

   this(real delegate() dg) { this.dg = dg; }
 }

 class B
 {
   real foo() { return 3.5; }
 }

 class C
 {
   real foo() { return 4.5; }
 }

 void main()
 {
   auto b = new B;
   auto a = new A(&b.foo);
   auto c = new C;
   a.fitness = &c.foo; // I want this to be an error
 }



 um... did you try encapsulation?

 class A
 {
    private real delegate() _dg;

    public real dg()
    {
       return _dg();
    }

    this(real delegate() dg) { this._dg = dg; }
 }

 -Steve



 This was the workaround I used as well.
 I don't like it because of the extra level of indirection (I end up
 calling 2 functions instead of 1).  I don't consider this very efficient
 or convenient.



I would have expected the dg() method (or property I guess) in the above to 
be inlined, possibly requiring a final specifier? In that case I don't see 
any reduction in performance.

As a matter of interest the following code is fairly equivalent but results 
in some bizarre property/delegate interaction:

class A
{
    private real delegate() _dg;

    this(real delegate() dg) { this._dg = dg; }

    public real delegate() dg()
    {
        return _dg;
    }
}

// Sample usage
public void example(real delegate() dg)
{
    A test = new A(dg);
    // test.dg        - Evaluates to the delegate dg
    // test.dg()     - Also evaluates to the delegate dg
    test.dg()()      // Required to actually execute the delegate
}

Neil
Feb 13 2008
parent reply Denton Cockburn <diboss hotmail.com> writes:
On Thu, 14 Feb 2008 08:53:23 +0900, Neil Vice wrote:


 
 "Denton Cockburn" <diboss hotmail.com> wrote in message 
 news:pan.2008.02.13.22.55.38.263151 hotmail.com...

 On Wed, 13 Feb 2008 14:33:33 -0500, Steven Schveighoffer wrote:


 "Denton Cockburn" wrote

 How do I do this?  I'm trying to create a class member here that needs 
 to
 be initialized in the constructor, but cannot be changed later.

 class A
 {
   (const doesn't work) real delegate() dg; // this is that
   function;

   this(real delegate() dg) { this.dg = dg; }
 }

 class B
 {
   real foo() { return 3.5; }
 }

 class C
 {
   real foo() { return 4.5; }
 }

 void main()
 {
   auto b = new B;
   auto a = new A(&b.foo);
   auto c = new C;
   a.fitness = &c.foo; // I want this to be an error
 }



 um... did you try encapsulation?

 class A
 {
    private real delegate() _dg;

    public real dg()
    {
       return _dg();
    }

    this(real delegate() dg) { this._dg = dg; }
 }

 -Steve



 This was the workaround I used as well.
 I don't like it because of the extra level of indirection (I end up
 calling 2 functions instead of 1).  I don't consider this very efficient
 or convenient.



 I would have expected the dg() method (or property I guess) in the above to 
 be inlined, possibly requiring a final specifier? In that case I don't see 
 any reduction in performance.
 
 As a matter of interest the following code is fairly equivalent but results 
 in some bizarre property/delegate interaction:
 
 class A
 {
     private real delegate() _dg;
 
     this(real delegate() dg) { this._dg = dg; }
 
     public real delegate() dg()
     {
         return _dg;
     }
 }
 
 // Sample usage
 public void example(real delegate() dg)
 {
     A test = new A(dg);
     // test.dg        - Evaluates to the delegate dg
     // test.dg()     - Also evaluates to the delegate dg
     test.dg()()      // Required to actually execute the delegate
 }
 
 Neil



isn't that because you have the function (test.dg) return a "real
delegate()" so: test.dg() returns a delegate, and test.dg()() calls that
delegate.
Feb 13 2008
parent "Neil Vice" <sardonicpresence gmail.com> writes:
"Denton Cockburn" <diboss hotmail.com> wrote in message 
news:pan.2008.02.14.00.52.40.389590 hotmail.com...

 On Thu, 14 Feb 2008 08:53:23 +0900, Neil Vice wrote:


 "Denton Cockburn" <diboss hotmail.com> wrote in message
 news:pan.2008.02.13.22.55.38.263151 hotmail.com...

 On Wed, 13 Feb 2008 14:33:33 -0500, Steven Schveighoffer wrote:


 "Denton Cockburn" wrote

 How do I do this?  I'm trying to create a class member here that needs
 to
 be initialized in the constructor, but cannot be changed later.

 class A
 {
   (const doesn't work) real delegate() dg; // this is that
   function;

   this(real delegate() dg) { this.dg = dg; }
 }

 class B
 {
   real foo() { return 3.5; }
 }

 class C
 {
   real foo() { return 4.5; }
 }

 void main()
 {
   auto b = new B;
   auto a = new A(&b.foo);
   auto c = new C;
   a.fitness = &c.foo; // I want this to be an error
 }



 um... did you try encapsulation?

 class A
 {
    private real delegate() _dg;

    public real dg()
    {
       return _dg();
    }

    this(real delegate() dg) { this._dg = dg; }
 }

 -Steve



 This was the workaround I used as well.
 I don't like it because of the extra level of indirection (I end up
 calling 2 functions instead of 1).  I don't consider this very efficient
 or convenient.



 I would have expected the dg() method (or property I guess) in the above 
 to
 be inlined, possibly requiring a final specifier? In that case I don't 
 see
 any reduction in performance.

 As a matter of interest the following code is fairly equivalent but 
 results
 in some bizarre property/delegate interaction:

 class A
 {
     private real delegate() _dg;

     this(real delegate() dg) { this._dg = dg; }

     public real delegate() dg()
     {
         return _dg;
     }
 }

 // Sample usage
 public void example(real delegate() dg)
 {
     A test = new A(dg);
     // test.dg        - Evaluates to the delegate dg
     // test.dg()     - Also evaluates to the delegate dg
     test.dg()()      // Required to actually execute the delegate
 }

 Neil



 isn't that because you have the function (test.dg) return a "real
 delegate()" so: test.dg() returns a delegate, and test.dg()() calls that
 delegate.



Yes, however by similar logic one could conclude that because the property 
"test.dg" returns a "real delegate()" that "test.dg()" should execute the 
delegate and return a real.
Feb 13 2008
prev sibling parent Derek Parnell <derek nomail.afraid.org> writes:
On Wed, 13 Feb 2008 10:59:26 -0500, Denton Cockburn wrote:


 How do I do this?  I'm trying to create a class member here that needs to
 be initialized in the constructor, but cannot be changed later.



The code below seems to work for me (DMD v2.008)

class A
{
   const real delegate() dg; // this is that function;

   this(const real delegate() dg) { this.dg = dg; }
}

class B
{
   real foo() { return 3.5; }
}

class C
{
   real foo() { return 4.5; }
}

void main()
{
   auto b = new B;
   auto a = new A(&b.foo);
   auto c = new C;
   a.dg = &c.foo; // correctly fails to compile.
}



-- 
Derek
(skype: derek.j.parnell)
Melbourne, Australia
14/02/2008 4:13:59 PM
Feb 13 2008