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digitalmars.D.learn - function overrides but is not covariant

reply "Namespace" <rswhite4 googlemail.com> writes:
That surprised me a bit. Is that expected?

----
import std.stdio;

struct A { }

interface IFoo {
	void bar(ref const A);
}

class Foo : IFoo {
	void bar(ref const A a) {
		
	}
	
	void bar(const A a) {
		return this.bar(a);
	}
}
----
prints:

Error: function c517.Foo.bar of type void(const(A) a) overrides 
but is not covariant with c517.IFoo.bar of type void(ref const(A))
Apr 28 2013
next sibling parent "Namespace" <rswhite4 googlemail.com> writes:
Nobody knows?
Apr 29 2013
prev sibling next sibling parent reply "John Colvin" <john.loughran.colvin gmail.com> writes:
On Sunday, 28 April 2013 at 19:45:41 UTC, Namespace wrote:

 That surprised me a bit. Is that expected?

 ----
 import std.stdio;

 struct A { }

 interface IFoo {
 	void bar(ref const A);
 }

 class Foo : IFoo {
 	void bar(ref const A a) {
 		
 	}
 	
 	void bar(const A a) {
 		return this.bar(a);
 	}
 }
 ----
 prints:

 Error: function c517.Foo.bar of type void(const(A) a) overrides 
 but is not covariant with c517.IFoo.bar of type void(ref 
 const(A))


Not surprising to me at all. Why would ref be covariant with 
non-ref?
Apr 29 2013
parent reply "Namespace" <rswhite4 googlemail.com> writes:
 Not surprising to me at all. Why would ref be covariant with 
 non-ref?


I do not understand the error fully. Why I cannot overload the 
method in the class with non-ref?
Apr 29 2013
parent "John Colvin" <john.loughran.colvin gmail.com> writes:
On Monday, 29 April 2013 at 09:23:01 UTC, Namespace wrote:

 Not surprising to me at all. Why would ref be covariant with 
 non-ref?


 I do not understand the error fully. Why I cannot overload the 
 method in the class with non-ref?


Sorry, my mistake, it looks like a bug. Dmd thinks that you're 
trying to override, not overload.
Apr 29 2013
prev sibling next sibling parent reply Timon Gehr <timon.gehr gmx.ch> writes:
On 04/28/2013 09:45 PM, Namespace wrote:

 That surprised me a bit. Is that expected?

 ----
 import std.stdio;

 struct A { }

 interface IFoo {
      void bar(ref const A);
 }

 class Foo : IFoo {
      void bar(ref const A a) {

      }

      void bar(const A a) {
          return this.bar(a);
      }
 }
 ----
 prints:

 Error: function c517.Foo.bar of type void(const(A) a) overrides but is
 not covariant with c517.IFoo.bar of type void(ref const(A))


Seems to be a bug.
Apr 29 2013
parent "Namespace" <rswhite4 googlemail.com> writes:
On Monday, 29 April 2013 at 11:40:45 UTC, Timon Gehr wrote:

 On 04/28/2013 09:45 PM, Namespace wrote:

 That surprised me a bit. Is that expected?

 ----
 import std.stdio;

 struct A { }

 interface IFoo {
     void bar(ref const A);
 }

 class Foo : IFoo {
     void bar(ref const A a) {

     }

     void bar(const A a) {
         return this.bar(a);
     }
 }
 ----
 prints:

 Error: function c517.Foo.bar of type void(const(A) a) 
 overrides but is
 not covariant with c517.IFoo.bar of type void(ref const(A))


 Seems to be a bug.


I filled a new bug report. But the title is broken because of the 
very nice copy functionality of my tablet.
Apr 29 2013
prev sibling parent =?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:
On 04/28/2013 12:45 PM, Namespace wrote:


 That surprised me a bit. Is that expected?

 ----
 import std.stdio;

 struct A { }

 interface IFoo {
      void bar(ref const A);
 }

 class Foo : IFoo {
      void bar(ref const A a) {

      }

      void bar(const A a) {
          return this.bar(a);
      }
 }
 ----
 prints:

 Error: function c517.Foo.bar of type void(const(A) a) overrides but is
 not covariant with c517.IFoo.bar of type void(ref const(A))


As others have said, one would expect this to compile because it is very 
common to overload on the same struct type, one taking by-value, the 
other taking by-reference. The former is mainly to capture rvalue struct 
objects and the latter is for lvalues.

To match what is common in Phobos and TDPL is to define the by-value 
overload without 'const':

     void bar(A a) {
         return this.bar(a);
     }

This example now compiles.

Ali
Apr 29 2013