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digitalmars.D.bugs - bug(?) with recursive aliases

reply Sean Kelly <sean f4.ca> writes:
I'm not sure whether this is a bug, but I haven't been able to find a 
syntax that works.  Notice that t.val!(0) is fine, so the problem is 
expanding "alias tail.val!(n-1) val":

C:\code\d>type test.d
void main()
{
     auto t = new Tuple!(int,Tuple!(int))();

     t.val!(0) = 1;
     t.val!(1) = 2;
}

struct Empty
{

}

class Tuple( HeadType, TailType = Empty )
{
     alias HeadType  Type;
     HeadType        head;
     TailType        tail;

     template val( int n )
     {
         static if( n == 0 )
             alias head val;
         else static if( is( typeof(tail) == Empty ) )
             alias tail val;
         else
             alias tail.val!(n-1) val;
     }
}
C:\code\d>dmd test
test.d(27): template identifier val is not a member of tail
test.d(6): template instance test.Tuple!(int,Tuple).Tuple.val!(1) error 
instantiating
test.d(6): cannot implicitly convert expression (2) of type int to 
test.Tuple!(int).Tuple

C:\code\d>


I also tried partial specialization, thinking the problem might be that 
Empty doesn't define a val template member:


C:\code\d>type test.d
void main()
{
     auto t = new Tuple!(int,Tuple!(int))();

     t.val!(0) = 1;
     t.val!(1) = 2;
}

struct Empty
{

}

class Tuple( HeadType, TailType = Empty )
{
     alias HeadType  Type;
     HeadType        head;
     TailType        tail;


     template val( int n, T : Empty = TailType )
     {
         static if( n == 0 )
             alias head val;
         else
             alias tail val;
     }

     template val( int n, T = TailType )
     {
         static if( n == 0 )
             alias head val;
         else
             alias tail.val!(n-1,TailType) val;
     }
}
C:\code\d>dmd test.d
test.d(34): template identifier val is not a member of tail
test.d(6): template instance test.Tuple!(int,Tuple).Tuple.val!(1) error 
instantiating
test.d(6): cannot implicitly convert expression (2) of type int to 
test.Tuple!(int).Tuple

C:\code\d>
Feb 09 2006
parent reply Sean Kelly <sean f4.ca> writes:
I think I'm merely running up against the limitations of 'alias' here. 
Can 'alias' be used to alias variables?  And if so, what are the 
restrictions?  The spec isn't of much use here.  For reference, here is 
a shortened test case that exhibits the problem.  Why can I alias 'i' 
but not 's.i'?  Is it merely a scope issue?

C:\code\d\bugs>type 145_2.d
void main()
{
     struct S { int i; }
     S   s;
     int i;

     alias i   a1;
     alias s.i a2;
}
C:\code\d\bugs>dmd 145_2.d
145_2.d(8): s.i is used as a type

C:\code\d\bugs>
Feb 09 2006
parent Thomas Kuehne <thomas-dloop kuehne.cn> writes:
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Hash: SHA1

Sean Kelly schrieb am 2006-02-10:

 I think I'm merely running up against the limitations of 'alias' here. 
 Can 'alias' be used to alias variables?  And if so, what are the 
 restrictions?  The spec isn't of much use here.  For reference, here is 
 a shortened test case that exhibits the problem.  Why can I alias 'i' 
 but not 's.i'?  Is it merely a scope issue?

 C:\code\d\bugs>type 145_2.d
 void main()
 {
      struct S { int i; }
      S   s;
      int i;

      alias i   a1;
      alias s.i a2;
 }
 C:\code\d\bugs>dmd 145_2.d
 145_2.d(8): s.i is used as a type


Added to DStress
http://dstress.kuehne.cn/run/a/alias_29_A.d
http://dstress.kuehne.cn/run/a/alias_29_B.d

Thomas


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Feb 11 2006