• Rene Zwanenburg (24/24) Jun 26 2014 I /think/ this is a bug, but I'm not 100% sure. The following
• John Colvin (13/37) Jun 26 2014 I don't think that's a bug, but I think the template constraint
• John Colvin (3/51) Jun 26 2014 Ah, it appears that this has already been done. Good.
• hane (2/26) Jun 26 2014 DMD 2.066(git head) compiled both without error.
• Rene Zwanenburg (2/3) Jun 26 2014 Thanks for checking!
• Meta (3/27) Jun 26 2014 Yes, this is a bug. This code should work. If it doesn't compile
• Rene Zwanenburg (3/5) Jun 26 2014 Apparently it does. I'm not set up to build DMD myself so I'm

"Rene Zwanenburg" <renezwanenburg gmail.com> writes:

I /think/ this is a bug, but I'm not 100% sure. The following 
compiles without any problems, as it should:

import std.typecons;

alias Handle(T) = RefCounted!(T, RefCountedAutoInitialize.no);

auto initialized(T)() if(is(T == RefCounted!S, S...))
{
	T refCounted;
	refCounted.refCountedStore.ensureInitialized();
	return refCounted;
}

alias S = Handle!S_Impl;
struct S_Impl
{
}

void main()
{
	auto s = initialized!S;
}


Change 'initialized' to:
auto initialized(T)() if(is(T == Handle!S, S))
and the compiler will complain:

Error: template instance test.initialized!(RefCounted!(S_Impl, 
cast(RefCountedAutoInitialize)0)) does not match template 
declaration initialized(T)() if (is(T == Handle!S, S))

"John Colvin" <john.loughran.colvin gmail.com> writes:

On Thursday, 26 June 2014 at 10:09:53 UTC, Rene Zwanenburg wrote:
 I /think/ this is a bug, but I'm not 100% sure. The following 
 compiles without any problems, as it should:

 import std.typecons;

 alias Handle(T) = RefCounted!(T, RefCountedAutoInitialize.no);

 auto initialized(T)() if(is(T == RefCounted!S, S...))
 {
 	T refCounted;
 	refCounted.refCountedStore.ensureInitialized();
 	return refCounted;
 }

 alias S = Handle!S_Impl;
 struct S_Impl
 {
 }

 void main()
 {
 	auto s = initialized!S;
 }


 Change 'initialized' to:
 auto initialized(T)() if(is(T == Handle!S, S))
 and the compiler will complain:

 Error: template instance test.initialized!(RefCounted!(S_Impl, 
 cast(RefCountedAutoInitialize)0)) does not match template 
 declaration initialized(T)() if (is(T == Handle!S, S))

I don't think that's a bug, but I think the template constraint 
itself shouldn't be legal to write. It's not possible to support 
the general case of a template A in is(T == A!X, X) as it would 
require following all possible instantiation paths of A.

The compiler could keep track of how a type was created on a 
per-identifier basis and then use that to check, but that would 
mean rejecting types that had a different instantiation path 
(e.g. is(RefCounted!(int, RefCountedAutoInitialize.no) == 
Handle!S, S) == false).

What might be feasible would be to extend is(T == A!X, X) to work 
with simple tmeplates and paramterised aliases like Handle, while 
statically disallowing more complicated / undecidable ones..

"John Colvin" <john.loughran.colvin gmail.com> writes:

On Thursday, 26 June 2014 at 12:38:40 UTC, John Colvin wrote:
 On Thursday, 26 June 2014 at 10:09:53 UTC, Rene Zwanenburg 
 wrote:
 I /think/ this is a bug, but I'm not 100% sure. The following 
 compiles without any problems, as it should:

 import std.typecons;

 alias Handle(T) = RefCounted!(T, RefCountedAutoInitialize.no);

 auto initialized(T)() if(is(T == RefCounted!S, S...))
 {
 	T refCounted;
 	refCounted.refCountedStore.ensureInitialized();
 	return refCounted;
 }

 alias S = Handle!S_Impl;
 struct S_Impl
 {
 }

 void main()
 {
 	auto s = initialized!S;
 }


 Change 'initialized' to:
 auto initialized(T)() if(is(T == Handle!S, S))
 and the compiler will complain:

 Error: template instance test.initialized!(RefCounted!(S_Impl, 
 cast(RefCountedAutoInitialize)0)) does not match template 
 declaration initialized(T)() if (is(T == Handle!S, S))

 I don't think that's a bug, but I think the template constraint 
 itself shouldn't be legal to write. It's not possible to 
 support the general case of a template A in is(T == A!X, X) as 
 it would require following all possible instantiation paths of 
 A.

 The compiler could keep track of how a type was created on a 
 per-identifier basis and then use that to check, but that would 
 mean rejecting types that had a different instantiation path 
 (e.g. is(RefCounted!(int, RefCountedAutoInitialize.no) == 
 Handle!S, S) == false).

 What might be feasible would be to extend is(T == A!X, X) to 
 work with simple tmeplates and paramterised aliases like 
 Handle, while statically disallowing more complicated / 
 undecidable ones..

Ah, it appears that this has already been done. Good.

If I've misunderstood the situation, somebody please correct me.

"hane" <han.ehit.suzi.0 gmail.com> writes:

On Thursday, 26 June 2014 at 10:09:53 UTC, Rene Zwanenburg wrote:
 I /think/ this is a bug, but I'm not 100% sure. The following 
 compiles without any problems, as it should:

 import std.typecons;

 alias Handle(T) = RefCounted!(T, RefCountedAutoInitialize.no);

 auto initialized(T)() if(is(T == RefCounted!S, S...))
 {
 	T refCounted;
 	refCounted.refCountedStore.ensureInitialized();
 	return refCounted;
 }

 alias S = Handle!S_Impl;
 struct S_Impl
 {
 }

 void main()
 {
 	auto s = initialized!S;
 }


 Change 'initialized' to:
 auto initialized(T)() if(is(T == Handle!S, S))
 and the compiler will complain:

 Error: template instance test.initialized!(RefCounted!(S_Impl, 
 cast(RefCountedAutoInitialize)0)) does not match template 
 declaration initialized(T)() if (is(T == Handle!S, S))

DMD 2.066(git head) compiled both without error.

"Rene Zwanenburg" <renezwanenburg gmail.com> writes:

On Thursday, 26 June 2014 at 12:52:54 UTC, hane wrote:
 DMD 2.066(git head) compiled both without error.

Thanks for checking!

"Meta" <jared771 gmail.com> writes:

On Thursday, 26 June 2014 at 10:09:53 UTC, Rene Zwanenburg wrote:
 I /think/ this is a bug, but I'm not 100% sure. The following 
 compiles without any problems, as it should:

 import std.typecons;

 alias Handle(T) = RefCounted!(T, RefCountedAutoInitialize.no);

 auto initialized(T)() if(is(T == RefCounted!S, S...))
 {
 	T refCounted;
 	refCounted.refCountedStore.ensureInitialized();
 	return refCounted;
 }

 alias S = Handle!S_Impl;
 struct S_Impl
 {
 }

 void main()
 {
 	auto s = initialized!S;
 }


 Change 'initialized' to:
 auto initialized(T)() if(is(T == Handle!S, S))
 and the compiler will complain:

 Error: template instance test.initialized!(RefCounted!(S_Impl, 
 cast(RefCountedAutoInitialize)0)) does not match template 
 declaration initialized(T)() if (is(T == Handle!S, S))

Yes, this is a bug. This code should work. If it doesn't compile 
with Git HEAD, you should file a bug report.

"Rene Zwanenburg" <renezwanenburg gmail.com> writes:

On Thursday, 26 June 2014 at 13:25:00 UTC, Meta wrote:
 Yes, this is a bug. This code should work. If it doesn't 
 compile with Git HEAD, you should file a bug report.

Apparently it does. I'm not set up to build DMD myself so I'm 
always just using the latest release.