Re: function overrides but is not covariant

[Namespace]

Nobody knows?

Re: function overrides but is not covariant

[John Colvin]

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?

Re: function overrides but is not covariant

[Namespace]

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?

Re: function overrides but is not covariant

[Timon Gehr]

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.

Re: function overrides but is not covariant

[John Colvin]

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.

Re: function overrides but is not covariant

[Ali Çehreli]

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

Re: function overrides but is not covariant

[Namespace]

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.