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digitalmars.D.bugs - [Issue 8657] New: TypeInfo generated for const/immutable static arrays not transitive

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=8657

           Summary: TypeInfo generated for const/immutable static arrays
                    not transitive
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: r.sagitario gmx.de


--- Comment #0 from Rainer Schuetze <r.sagitario gmx.de> 2012-09-14 01:29:37
PDT ---
This test program

import std.stdio;

void test(T)()
{
    T p;
    writeln("==============");
    writeln("p: ", typeid(p));
    TypeInfo ti = typeid(p);
    TypeInfo_Const cti = cast(TypeInfo_Const)ti;
    writeln("p[0] : ", typeid(p[0]));
    writeln("ti.next : ", cast(TypeInfo)ti.next); // cannot write
const(TypeInfo)
    writeln("cti.base : ", cti.next);
}

void testMod(T)()
{
    test!(const(T))();
    test!(immutable(T))();
    test!(shared(T))();
}

void main()
{
    testMod!(int*)();
    testMod!(int[])();
    testMod!(int[2])();
//    testMod!(int[2][3])();
}

outputs:
==============
p: const(const(int)*)
p[0] : const(int)
ti.next : const(int)
cti.base : const(int)*
==============
p: immutable(immutable(int)*)
p[0] : immutable(int)
ti.next : immutable(int)
cti.base : immutable(int)*
==============
p: shared(shared(int)*)
p[0] : shared(int)
ti.next : shared(int)
cti.base : shared(int)*
==============
p: const(const(int)[])
p[0] : const(int)
ti.next : const(int)
cti.base : const(int)[]
==============
p: immutable(immutable(int)[])
p[0] : immutable(int)
ti.next : immutable(int)
cti.base : immutable(int)[]
==============
p: shared(shared(int)[])
p[0] : shared(int)
ti.next : shared(int)
cti.base : shared(int)[]
==============
p: const(int[2])
p[0] : const(int)
ti.next : int
cti.base : int[2]
==============
p: immutable(int[2])
p[0] : immutable(int)
ti.next : int
cti.base : int[2]
==============
p: shared(shared(int)[2])
p[0] : shared(int)
ti.next : shared(int)
cti.base : shared(int)[2]

It shows that the next and base properties of the TypeInfo generated for
const(int[2]) and immutable(int[2]) lose the qualifier. This does not happen
for "shared".

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--- Comment #1 from Kenji Hara <k.hara.pg gmail.com> 2012-09-16 04:47:16 PDT ---
(In reply to comment #0)
[snip]

 It shows that the next and base properties of the TypeInfo generated for
 const(int[2]) and immutable(int[2]) lose the qualifier. This does not happen
 for "shared".


I think this is expected behavior, because const(int[2]) is value type.

TypeInfo_Const.next specifies the TypeInfo object of the type that removed head
const qualifier from original type.
And, Removing const from const(int[2]) is int[2], not const(int)[2].
It's just same as std.traits.Unqual.

  pragma(msg, Unqual!(const(int[2])));  // prints const(int)[]
  pragma(msg, Unqual!(const(int[2])));  // prints int[2]

Additionally, const(int)[2] is same as const(int[2]). There is just a
syntactically difference.

  alias const(int)[2] T1;
  alias const(int[2]) T2;
  static assert(is(T1 == T2));  // they are same
  pragma(msg, T1);   // prints const(int[2])
  pragma(msg, T2);   // prints const(int[2])

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--- Comment #2 from Rainer Schuetze <r.sagitario gmx.de> 2012-09-16 10:23:53
PDT ---
(In reply to comment #1)

 (In reply to comment #0)
 [snip]
 TypeInfo_Const.next specifies the TypeInfo object of the type that removed head
 const qualifier from original type.


Please note the difference between base and next (as used in object_.d, see
also issue 8656 for naming confusion). What you describe is
"TypeInfo_Const.base", though called "next" in object.di. As can be seen from
the other types, TypeInfo.next does the indirection and yields the type of the
element pointed to or in the array.


 And, Removing const from const(int[2]) is int[2], not const(int)[2].
 It's just same as std.traits.Unqual.
 
   pragma(msg, Unqual!(const(int[2])));  // prints const(int)[]
   pragma(msg, Unqual!(const(int[2])));  // prints int[2]


I fail to spot the difference between the two statement ;-) I guess you meant
to remove the 2 in the first line.


 
 Additionally, const(int)[2] is same as const(int[2]). There is just a
 syntactically difference.


That could also support my point of view: I'd very much expect
(cast(TypeInfo)typeid(const(int)[2])).next to be typeid(const(int)). Maybe the
runtime type information of a static array should be typed that way to start
with.

Even if I cannot convince you: What do you think about the transitivity of the
shared modifier in the example. Is it wrong then?

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