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digitalmars.D - Re: Static operator overloads are possible why?

reply Giles Bathgate <gilesbathgate gmail.com> writes:
 You can access static class members through variables which are of that 
 class's type.  This applies to all static methods and fields; static 
 operator overloads are no exception.  I'm not entirely sure why you can do 
 this; it's probably "the way C++ does it."




I don't know what you mean by this I tried

public class Test
{
    public char[] Name;

    public Test opAddAssign(Test value)
    {
        writefln(value.Name);
        writefln(Test.Name);
        //...
    }
}

It didnt work


 That being said, I'm not sure why you decided to try a static overload 
 instead of just new'ing t.  Another solution would be to make your multicast 
 delegate a struct type instead, which wouldn't have to be new'ed; I think 
 DFL (very .Net like form library for D) does this. 



DFL huh? there is another thing that went under the radar... Its a shame there
is no "distribution" of D

Anyway I am not looking for a solution to the problem of how to create a
multicast delegate class in D I am trying to solve the meta problem, of how to
access an lvalue in a static operator overload.
Jul 05 2007
parent reply Manfred Nowak <svv1999 hotmail.com> writes:
Giles Bathgate wrote


 how to access an lvalue in a static operator overload.



parameters or declared `static' too. Therefore change

|    public char[] Name;

to

     public static char[] Name;

Or as a complete example:

public class Test
{
	static char[] baseName = "Test";
	char[] name;

	static void opAddAssign(Test value)
	{
		writefln(value.name);
		Test.baseName~= ".".dup;
		baseName~= value.name.dup;
	}
	static void opCall(){
		writefln( ":", baseName);
	}
} 

void main()
{
	Test b = new Test();
	b.name = "foo";

	Test += b;
	Test();

     Test t;
     t(); 
}
import std.stdio;

Or in other words:
for the entities of a class that are declared `static' the D-compiler 
automatically establishes a singleton and that singleton can be 
accessed 
1) by the name of the class or
2) every instance of the class

So:  your questions

 'should static operator overloads even be allowed?' and if they
 were to be allowed should they not have two arguments?



-manfred
Jul 05 2007
next sibling parent GilesBathgate <gilesbathgate gmail.com> writes:
 operators declared `static' can only access entities that are actual 
 parameters or declared `static' too. 



Exactly and since the lvalue is not a parameter then I cannot access it!

The language dosen't support what I want to do, and I am preposing it should
because its very useful if not essential to be able to access the lvalue in an
operator overload.
Jul 05 2007
prev sibling parent reply GilesBathgate <gilesbathgate gmail.com> writes:
 Or in other words:
 for the entities of a class that are declared `static' the D-compiler 
 automatically establishes a singleton and that singleton can be 
 accessed 
 1) by the name of the class or
 2) every instance of the class



Yeah I know, I am a programmer.

If you can translate this C# code into D I will give you a medal

     public class Test
        {
            public string Name;

            public static Test operator +(Test lvalue, Test rvalue)
            {
                if (lvalue == null) { lvalue = new Test(); lvalue.Name = "foo";
}
                if (rvalue == null) { rvalue = new Test(); rvalue.Name = "bar";
}

                Console.Write(lvalue.Name);
                Console.Write(rvalue.Name);

                return rvalue;
            }

        }

static void Main(string[] args)
        {
            Test T = null;
            Test B = null;
            T += B;
        }
Jul 05 2007
next sibling parent reply Derek Parnell <derek psych.ward> writes:
On Thu, 05 Jul 2007 15:24:34 -0400, GilesBathgate wrote:



 If you can translate this C# code into D I will give you a medal



Where do I apply for the medal :-)

import std.stdio;
class Test
{
    string Name;

    static Test opAddAssign(ref Test lvalue, ref Test rvalue)
    {
        if (lvalue is null)
        {
            lvalue = new Test();
            lvalue.Name = "foo";
        }
        if (rvalue is null)
        {
            rvalue = new Test();
            rvalue.Name = "bar";
        }

        writefln("%s", lvalue.Name);
        writefln("%s", rvalue.Name);

        return rvalue;
    }
}

void main()
{
    Test T;
    Test B;
    Test.opAddAssign(T,B);
}

-- 
Derek Parnell
Melbourne, Australia
skype: derek.j.parnell
Jul 05 2007
parent reply Giles Bathgate <gilesbathgate gmail.com> writes:
 void main()
 {
     Test T;
     Test B;
     Test.opAddAssign(T,B);
 }



Cheaters do not win medals. Its hardly an operator overload if you have to
write Test.opAddAssign(T,B); instead of T += B; sorry.

Do you see my point yet?
Jul 06 2007
parent reply Derek Parnell <derek psych.ward> writes:
On Fri, 06 Jul 2007 05:46:01 -0400, Giles Bathgate wrote:


 void main()
 {
     Test T;
     Test B;
     Test.opAddAssign(T,B);
 }



 Cheaters do not win medals. Its hardly an operator overload if you have to
write Test.opAddAssign(T,B); instead of T += B; sorry.
 Do you see my point yet?



Hang on a minute, all you asked for was someone to "translate" the C# code
into D. And that is what I did. You did not specify that the resultant
translation must use the "+=" operator. Do you see my point? <G>



-- 
Derek Parnell
Melbourne, Australia
skype: derek.j.parnell
Jul 06 2007
parent David L. Davis <SpottedTiger yahoo.com> writes:
Give the man his medal! :)  (It's not creating, if you follow the rules)

Derek Parnell Wrote:


 On Fri, 06 Jul 2007 05:46:01 -0400, Giles Bathgate wrote:
 

 void main()
 {
     Test T;
     Test B;
     Test.opAddAssign(T,B);
 }



 Cheaters do not win medals. Its hardly an operator overload if you have to
write Test.opAddAssign(T,B); instead of T += B; sorry.
 Do you see my point yet?



 Hang on a minute, all you asked for was someone to "translate" the C# code
 into D. And that is what I did. You did not specify that the resultant
 translation must use the "+=" operator. Do you see my point? <G>
 
 
 
 -- 
 Derek Parnell
 Melbourne, Australia
 skype: derek.j.parnell
Jul 06 2007
prev sibling parent Manfred Nowak <svv1999 hotmail.com> writes:
GilesBathgate wrote


 If you can translate this C# code into D I will give you a medal



As some replies might have shown, it is unclear what you might mean 
with "translate".

<elaboration>
In a game with main language german a german tourist in China asks a 
passerby "Sprechen Sie deutsch?", which means "Do you speak german?"

The correct _translation_ to english would of course be "Do you speak 
german?" But why would a native english speaker ask some one in China 
whether he speaks german?

So: the correct _transduction_ would be "Do you speak english?"

Because you are a programmer this elaboration should be enough to put 
you on the tip of the iceberg.  
</elaboration>

-manfred
Jul 08 2007