Hello,

In C++, you can overload methods by the constness of the method itself:

	class Foo
	{
		void bar ();		// #1
		void bar () const;	// #2
	}
	...
	Foo f;		f.bar();	// calls #1
	const Foo g;	g.bar();	// calls #2

I am wondering if there is any way to get similiar functionality in D? I have tried the following:

	class Foo
	{
		void bar () { ... }
		const void bar () { ... }
	}

but get a compiler error that the "bar"s conflict.

Why would I want to do this, you might ask?  Well, I would like to use this to write a pair of opSlice methods.  With built-in arrays, you can do this:

	char[] str = "Hello, world".dup;
	char[] substr = str[0..5];
	
	const(char)[] str2 = "Hello, world";
	const(char)[] substr2 = str2[0..5];
	char[] substr3 = str2[0..5]; 	// fails

i.e., the slice returns either a char[] or a const(char)[] depending on the constness of the array.  However, I cannot see how to make my own classes do the same thing, unless I can overload opSlice by constness.

Thanks,
Nathan Reed

Nathan Reed wrote:
> but get a compiler error that the "bar"s conflict.
Unfortunately (AFAIK) the symbol mangler doesn't take const into account yet, so it's impossible to overload like that until mangling is changed. :( I suspect Walter is hesitant to completely break library compatibility from D 1.0 to D 2.0! That's the problem with const correctness... gotta do it all the way or not at all... ;)

Perhaps this should be posted as a bug?

"Nathan Reed" <nathaniel.reed@gmail.com> wrote in message news:faga07$hj9$1@digitalmars.com...
> Hello,
>
> In C++, you can overload methods by the constness of the method itself:
>
> class Foo
> {
> void bar (); // #1
> void bar () const; // #2
> }
> ...
> Foo f; f.bar(); // calls #1
> const Foo g; g.bar(); // calls #2
>
> I am wondering if there is any way to get similiar functionality in D? I have tried the following:
>
> class Foo
> {
> void bar () { ... }
> const void bar () { ... }
> }
>
> but get a compiler error that the "bar"s conflict.
>
> Why would I want to do this, you might ask?  Well, I would like to use this to write a pair of opSlice methods.  With built-in arrays, you can do this:
>
> char[] str = "Hello, world".dup;
> char[] substr = str[0..5];
>
> const(char)[] str2 = "Hello, world";
> const(char)[] substr2 = str2[0..5];
> char[] substr3 = str2[0..5]; // fails
>
> i.e., the slice returns either a char[] or a const(char)[] depending on the constness of the array.  However, I cannot see how to make my own classes do the same thing, unless I can overload opSlice by constness.
>
> Thanks,
> Nathan Reed

Dnia Wed, 22 Aug 2007 14:20:19 -0500
"Craig Black" <cblack@ara.com> napisał/a:

> Perhaps this should be posted as a bug?
> 

This isn't bug.

Look also at the http://s3.amazonaws.com/dconf2007/WalterAndrei.pdf

page 38.


regards.

-- 
Witold Baryluk, aleph0
MAIL: baryluk@smp.if.uj.edu.pl
JID: movax@jabber.autocom.pl

Witold Baryluk wrote:
> 
> This isn't bug.
> 
> Look also at the http://s3.amazonaws.com/dconf2007/WalterAndrei.pdf
> 
> page 38.

Good, I'm glad to see this problem is being addressed.  I do have a question about the 'return' storage-class, though.  Will it only work for non-member functions, or will there be a syntax for writing a member function for which 'this' has the 'return' storage-class?  Although, with the new interchangeable function call syntax, this doesn't matter that much...

Thanks,
Nathan Reed