• Daniel Donnelly (27/27) Mar 27 2012 I have: [code]
• Daniel Donnelly (5/5) Mar 27 2012 The two solutions are:
• Steven Schveighoffer (15/19) Mar 27 2012 This transfers the constancy from the object to the result. Is that wha...
• bearophile (4/7) Mar 27 2012 Any space for compiler error message improvements here?
• denizzzka (2/7) Oct 09 2012 +1, spent two hours with a similar problem
• Lee Braiden (5/15) Feb 06 2013 +2. I wasted a little time on this too. Not much, but
• Timon Gehr (8/23) Feb 06 2013 I am writing a D compiler front end, and currently the following message...
• Lee Braiden (6/12) Feb 07 2013 Almost, it's definitely better, but what's wrong with:

"Daniel Donnelly" <enjoysmath gmail.com> writes:

I have: [code]

         module A;

	interface B {
	   public:
		  immutable B dup();
	}

	class A : B {
	   public:
		  this() {}
		  this(in char[] field) { this.field = field.dup; }
		  immutable A dup() { return new A(field); }
	   private:
		  char[] field;
	}

	void main()
	{
		B f, g;
		f = new A;
		g = new A;
		
		f = g.dup;
	}
[/code]

Compile: dmd A

Compile Output:
A.d(23): Error: function A.B.dup () immutable is not callable 
using argument types ()

"Daniel Donnelly" <enjoysmath gmail.com> writes:

The two solutions are:

inout(A) dup() inout { ... }
A dup() const { ... }

I'm using the latter.  Basically all I need is to copy any 
object: const, immut-, or mutable.

"Steven Schveighoffer" <schveiguy yahoo.com> writes:

On Tue, 27 Mar 2012 04:49:57 -0400, Daniel Donnelly <enjoysmath gmail.com>  
wrote:

 The two solutions are:

 inout(A) dup() inout { ... }

This transfers the constancy from the object to the result.  Is that what  
you want?  For arrays, dup means "return mutable", no matter what  
constancy it is called on.

 I'm using the latter.  Basically all I need is to copy any object:  
 const, immut-, or mutable.

BTW, here is what the compiler is complaining about:

immutable B dup();

This is a member function, with the attribute immutable.  What this does  
is specify that the hidden 'this' pointer is immutable.  It's equivalent  
to this:

B dup(immutable(B) this);

So what the compiler is saying is that you can't call dup with arguments  
(), you must call it with arguments '() immutable', meaning you must call  
it on an immutable B, not a mutable B.

-Steve

"bearophile" <bearophileHUGS lycos.com> writes:

Steven Schveighoffer:

 So what the compiler is saying is that you can't call dup with 
 arguments (), you must call it with arguments '() immutable', 
 meaning you must call it on an immutable B, not a mutable B.

Any space for compiler error message improvements here?

Bye,
bearophile

"denizzzka" <4denizzz gmail.com> writes:

On Tuesday, 27 March 2012 at 12:57:18 UTC, bearophile wrote:
 Steven Schveighoffer:

 So what the compiler is saying is that you can't call dup with 
 arguments (), you must call it with arguments '() immutable', 
 meaning you must call it on an immutable B, not a mutable B.

 Any space for compiler error message improvements here?

+1, spent two hours with a similar problem

"Lee Braiden" <leebraid gmail.com> writes:

On Tuesday, 9 October 2012 at 22:47:16 UTC, denizzzka wrote:
 On Tuesday, 27 March 2012 at 12:57:18 UTC, bearophile wrote:
 Steven Schveighoffer:

 So what the compiler is saying is that you can't call dup 
 with arguments (), you must call it with arguments '() 
 immutable', meaning you must call it on an immutable B, not a 
 mutable B.

 Any space for compiler error message improvements here?

 +1, spent two hours with a similar problem

+2.  I wasted a little time on this too.  Not much, but 
frustratingly more than necessary.

Why someone would write that error message makes SOME sense when 
explained, but the error message itself is still non-sensical ;)

Timon Gehr <timon.gehr gmx.ch> writes:

On 02/07/2013 12:13 AM, Lee Braiden wrote:
 On Tuesday, 9 October 2012 at 22:47:16 UTC, denizzzka wrote:
 On Tuesday, 27 March 2012 at 12:57:18 UTC, bearophile wrote:
 Steven Schveighoffer:

 So what the compiler is saying is that you can't call dup with
 arguments (), you must call it with arguments '() immutable',
 meaning you must call it on an immutable B, not a mutable B.

 Any space for compiler error message improvements here?

 +1, spent two hours with a similar problem

 +2.  I wasted a little time on this too.  Not much, but frustratingly
 more than necessary.

 Why someone would write that error message makes SOME sense when
 explained, but the error message itself is still non-sensical ;)

I am writing a D compiler front end, and currently the following message 
is displayed for the example:

A.d:22:9: error: receiver for member function 'dup' is unqualified, but 
'immutable' is required
     f = g.dup;
         ^~~~~

Is this what you'd want?

Lee Braiden <leebraid gmail.com> writes:

On Thu, 07 Feb 2013 00:31:20 +0100, Timon Gehr wrote:
 A.d:22:9: error: receiver for member function 'dup' is unqualified, but
 'immutable' is required
      f = g.dup;
          ^~~~~
 
 Is this what you'd want?

Almost, it's definitely better, but what's wrong with:

	"immutable object method dup cannot be called on mutable object d"

? ;)


-- 
Lee