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digitalmars.D.bugs - [Issue 4042] New: Unable to instantiate a struct template.

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=4042

           Summary: Unable to instantiate a struct template.
           Product: D
           Version: unspecified
          Platform: Other
        OS/Version: Linux
            Status: NEW
          Severity: blocker
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: e.insafutdinov gmail.com



10:25:58 PDT ---
Created an attachment (id=598)
testcase

When compiling the attached code I get

main.d(51): Error: this for ref_ needs to be type QList not type
QList!(QGraphicsWidget)
main.d(51): Error: struct main.QList!(QGraphicsWidget).QList member ref_ is not
accessible

This bug caused a lot of headache and held off development of QtD for quite a
while. I was finally able to reduce it to the sensible sized
test-case(originally the number of source files was about 500). If you play
with the testcase you'll find out that even slight modifications will lead to
change of the error message or to disappearing of it. Something is going
horribly wrong in the compiler. The version I tested it with is 2.042 which is
not present on the list.

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Apr 02 2010
next sibling parent reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=4042


Max Samukha <samukha voliacable.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |samukha voliacable.com



PDT ---
A corrected and smaller test-case:

template isQObjectType(T)
{
    enum isQObjectType = is(T.__isQObjectType);
}

template QTypeInfo(T)
{
    static if (!isQObjectType!T)
    {       
        enum size = T.sizeof;
    }
}

struct QList(T)
{
    alias QTypeInfo!T TI;
    int x;

    void foo()
    {
        x++;
    }
}

void exec(QList!(QAction) actions) {}

interface IQGraphicsItem
{
}

abstract class QGraphicsObject : IQGraphicsItem
{
}

class QGraphicsWidget : QGraphicsObject
{
}

class QAction
{
    final void associatedGraphicsWidgets(QList!(QGraphicsWidget) a)
    {
        QList!(QGraphicsWidget) x;
    }
}

void main()
{
}
----

There may be more than one bug. Note that the static if body in QTypeInfo is
evaluated even though no __isQObjectType is defined in QGraphicsWidget or
QAction.

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Apr 03 2010
parent wrzosk <dprogr gmail.com> writes:
The test case compiles when exec method definition is moved down:
template isQObjectType(T)
{
     enum isQObjectType = is(T.__isQObjectType);
}

template QTypeInfo(T)
{
     static if (!isQObjectType!T)
     {
         enum size = T.sizeof;
     }
}

struct QList(T)
{
     alias QTypeInfo!T TI;
     int x;

     void foo()
     {
         x++;
     }
}


interface IQGraphicsItem
{
}
void exec(QList!(QAction) actions) {}

abstract class QGraphicsObject : IQGraphicsItem
{
}

class QGraphicsWidget : QGraphicsObject
{
}

class QAction
{
     final void associatedGraphicsWidgets(QList!(QGraphicsWidget) a)
     {
         QList!(QGraphicsWidget) x;
     }
}

void main()
{
}
Apr 03 2010
prev sibling next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=4042




PDT ---

 There may be more than one bug. Note that the static if body in QTypeInfo is
 evaluated even though no __isQObjectType is defined in QGraphicsWidget or
 QAction.


Ignore that part. It's the other way around. If we add, for example, "alias
void __isQObjectType;" to QGraohicsWidget/QAction, the "static if" condition is
satisfied in QTypeInfo, though it should not.

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Apr 03 2010
prev sibling next sibling parent d-bugmail puremagic.com writes:
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Walter Bright <bugzilla digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bugzilla digitalmars.com



17:56:02 PDT ---
Thanks for the reduced test case.

This is a rather nasty problem. The essence of it is that when the
is(T.__isQObjectType) is evaluated, T is forward referenced. So it attempts to
forward instantiate T. This fails, and so the IsExpression fails.

The problem is that in the attempt to forward instantiate T, it doesn't quite
reset itself back to the state it was in before the IsExpression, and now parts
of the symbol table are in an "error" state, and a cascaded error message
(hence incomprehensible) comes out as a result.

A workaround is to remove 'abstract' from the class declaration, which enables
the forward instantiation to succeed.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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19:53:56 PDT ---
Trying to perfectly unwind forward reference failures is buggy and probably
doomed. This one fails because function parameter types don't get redone. While
it's easy to fix that one, there are just more lurking. A better approach is to
make forward references always work, something I've been working towards for a
while.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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20:00:03 PDT ---
changelog 477

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03:31:35 PDT ---


 changelog 477


Thanks for that. I will check if it fixes our problem later today. And I am
also looking forward to properly fix of forward references. This particular bug
may be fixed, but who knows if other will appear. It still persists as a
serious problem to me. Eliminating forward references completely will increase
the quality of the compiler significantly.

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May 10 2010
prev sibling next sibling parent d-bugmail puremagic.com writes:
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PDT ---
*** Issue 4043 has been marked as a duplicate of this issue. ***

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May 10 2010
prev sibling next sibling parent d-bugmail puremagic.com writes:
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PDT ---


 changelog 477


Qtd compiles with that. Thank you.

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May 10 2010
prev sibling parent d-bugmail puremagic.com writes:
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Don <clugdbug yahoo.com.au> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED



FixedDMD2.046.

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May 18 2010