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digitalmars.D.bugs - [Issue 9051] New: [CTFE] Working with non-trivial immutable globals?

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=9051

           Summary: [CTFE] Working with non-trivial immutable globals?
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: dmitry.olsh gmail.com



12:50:42 PST ---
I'm wondering if this is supposed to work. By all means I don't see why it has
to try this(this) in this case (and moreover fail).

struct Set{
    uint[] arr;
    this(this){  } //comment out to make it compile
}

pure auto getMeASet(uint[] arr)
{
    return Set(arr);
}

immutable set = getMeASet([1,2,3,4]);

pure auto getSecond(in Set set)
{
    return set.arr[1];
}

pragma(msg, getSecond(set));

And the diagnostic spits all kinds of nonsense:

D:\D\ctfe_glob.d(20): Error: variable ctfe_glob.__cpcttmp6 of type struct
const(Set) uses this(this), which is not allowed in static initialization
D:\D\ctfe_glob.d(20):        while evaluating pragma(msg, getSecond((const
const(Set) __cpcttmp6 = Set([1u, 2u, 3u, 4u]);
 , __cpcttmp6)))

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next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=9051


Don <clugdbug yahoo.com.au> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic
            Summary|[CTFE] Working with         |Passing an immutable global
                   |non-trivial immutable       |with post-blit to a CTFE
                   |globals?                    |function



The error message is not coming from CTFE. Here's a simple case from a comment
in the compiler source code (declaration.c):

/* The problem is the following code:
*  struct CopyTest {
*     double x;
*     this(double a) { x = a * 10.0;}
*     this(this) { x += 2.0; }
*  }
*  const CopyTest z = CopyTest(5.3);  // ok
*  const CopyTest w = z;              // not ok, postblit not run
*  static assert(w.x == 55.0);
* because the postblit doesn't get run on the initialization of w.
*/

I think that if we didn't call this(this), wrong code would result.
There is at least a diagnostic bug here - if it must behave this way, the code
that creates the comma expression should be issuing the error.

Interestingly, if you move it inside a function, the result is different:

void foo()
{
   pragma(msg, getSecond(set));
}

qqq.d(19): Error: static variable set cannot be referenced at compile time
qqq.d(19):        called from here: __cpcttmp6.__cpctor(set)
qqq.d(19):        called from here: getSecond((const const(Set) __cpcttmp6 =
__cpcttmp6.__cpctor(set);
 , __cpcttmp6))

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prev sibling next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=9051




10:49:17 PST ---


 The error message is not coming from CTFE. Here's a simple case from a comment
 in the compiler source code (declaration.c):
 
 /* The problem is the following code:
 *  struct CopyTest {
 *     double x;
 *     this(double a) { x = a * 10.0;}
 *     this(this) { x += 2.0; }
 *  }
 *  const CopyTest z = CopyTest(5.3);  // ok
 *  const CopyTest w = z;              // not ok, postblit not run
 *  static assert(w.x == 55.0);
 * because the postblit doesn't get run on the initialization of w.
 */
 
 I think that if we didn't call this(this), wrong code would result.


I agree in general. And But given that getMeASet(uint[] arr) is an r-value.
Surely the result of it should be just moved?

The other thought is: can't this(this) be run at compile-time then? What are
limitations?


 There is at least a diagnostic bug here - if it must behave this way, the code
 that creates the comma expression should be issuing the error.
 
 Interestingly, if you move it inside a function, the result is different:
 


The same thing happens if you try passing set by reference be it const or
otherwise.


 void foo()
 {
    pragma(msg, getSecond(set));
 }
 
 qqq.d(19): Error: static variable set cannot be referenced at compile time
 qqq.d(19):        called from here: __cpcttmp6.__cpctor(set)
 qqq.d(19):        called from here: getSecond((const const(Set) __cpcttmp6 =
 __cpcttmp6.__cpctor(set);
  , __cpcttmp6))


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prev sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=9051








 The error message is not coming from CTFE. Here's a simple case from a comment
 in the compiler source code (declaration.c):
 
 /* The problem is the following code:
 *  struct CopyTest {
 *     double x;
 *     this(double a) { x = a * 10.0;}
 *     this(this) { x += 2.0; }
 *  }
 *  const CopyTest z = CopyTest(5.3);  // ok
 *  const CopyTest w = z;              // not ok, postblit not run
 *  static assert(w.x == 55.0);
 * because the postblit doesn't get run on the initialization of w.
 */
 
 I think that if we didn't call this(this), wrong code would result.


 
 I agree in general. And But given that getMeASet(uint[] arr) is an r-value.
 Surely the result of it should be just moved?
 
 The other thought is: can't this(this) be run at compile-time then? What are
 limitations?


Yeah, that's kind of like bug 7988. The calling of this(this) should be part of
the CTFE'd bit. CTFE could cope with it, no problem, it just doesn't get a
chance. BTW if we moved the this(this) into CTFE, the example I posted would
also work!

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