[Issue 1432] Bogus "overlapping initialization" error with structs, unions, and member initializers

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https://issues.dlang.org/show_bug.cgi?id=1432

Iain Buclaw  changed:

   What|Removed |Added

   Priority|P2  |P3

--

[Issue 1432] Bogus "overlapping initialization" error with structs, unions, and member initializers

[d-bugmail--- via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=1432

Iain Buclaw  changed:

   What|Removed |Added

 Status|RESOLVED|REOPENED
 CC||ibuc...@gdcproject.org
 Resolution|FIXED   |---

--- Comment #9 from Iain Buclaw  ---
This issue seems to be closed for the wrong reason.

>From runnable/structlit.d:
---
union U7727A3 { int i;   double d = 2.5; }

union U7727B3 { double d;   int i = 123; }


void test7727()
{
import core.stdc.math : isnan;

// Blocked by https://issues.dlang.org/show_bug.cgi?id=1432
{ U7727A3 u;assert(u.d == 2.5); }
{ U7727A3 u = { i: 1024 };  assert(u.i == 1024); }
{ U7727A3 u = { d: 1.225 }; assert(u.d == 1.225); }
  static assert(!__traits(compiles,
{ U7727A3 u = { i: 1024, d: 1.225 }; }
  ));

// Blocked by https://issues.dlang.org/show_bug.cgi?id=1432
{ U7727B3 u;assert(u.i == 123); }
{ U7727B3 u = { i: 1024 };  assert(u.i == 1024); }
{ U7727B3 u = { d: 1.225 }; assert(u.d == 1.225); }
  static assert(!__traits(compiles,
{ U7727B3 u = { i: 1024, d: 1.225 }; }
  ));
}

--

[Issue 1432] Bogus "overlapping initialization" error with structs, unions, and member initializers

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https://issues.dlang.org/show_bug.cgi?id=1432

Simen Kjaeraas  changed:

   What|Removed |Added

 Status|NEW |RESOLVED
 CC||simen.kja...@gmail.com
 Resolution|--- |FIXED

--- Comment #8 from Simen Kjaeraas  ---
This works in 2.075.1.

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[Issue 1432] Bogus overlapping initialization error with structs, unions, and member initializers

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https://d.puremagic.com/issues/show_bug.cgi?id=1432


Martin Nowak c...@dawg.eu changed:

   What|Removed |Added

 CC||c...@dawg.eu


--- Comment #5 from Martin Nowak c...@dawg.eu 2013-12-16 00:10:49 PST ---
Do we have a distinction between explicit and implicit initialization somewhere
else in the language?
Otherwise it's idfficult to explain, why these two differ.
union { int a; string b = s; }
union { int a = 0; string b = s; }

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[Issue 1432] Bogus overlapping initialization error with structs, unions, and member initializers

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--- Comment #6 from Kenji Hara k.hara...@gmail.com 2013-12-16 00:51:07 PST ---
(In reply to comment #5)
 Do we have a distinction between explicit and implicit initialization 
 somewhere
 else in the language?
 Otherwise it's idfficult to explain, why these two differ.
 union { int a; string b = s; }
 union { int a = 0; string b = s; }

I think the main argument of this issue is, that explicitly initialized
overlapped field should be always preferred than default initializing.

The two concepts, overlapping fields and default initializing behavior for
safely programming is normally conflict each other, because Compiler cannot
initialize all of overlapped fields by default.
Therefore, D language should specially treat overlapped fields.

For union U { T1 f1; T2 f2; ... }, T1.init is picked for the default
initializer of overlapped fields.
I think it is legitimate behavior because it is C-compatible.

However, if only one overlapped fields are explicitly initialized by
programmer, current dmd behaves foolish.

  union U1 { T1 f1 = x; T2 f2; }
  // x is used for default initializer

  union U2 { T1 f1; T2 f2 = x; }
  // x conflicts with implicitly picked default initializer T1.init !

This is D-specific case, and I think the current behavior is contrary to the
two D language concepts -
1. If programmer specifies something explicitly, compiler should respect it.
2. If it is unnecessary, order dependent feature is not good.

In the U2 case, programmer explicitly add a initializer for the overlapped
field f2. So, I think compiler should pick it.

Of course, two or more overlapped fields have explicit initializers, it should
be an error.

  union U3 { T1 f1 = x; T2 f2 = y;
  // explicit specified initializers x and y conflicts each other

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--- Comment #7 from Martin Nowak c...@dawg.eu 2013-12-16 12:52:04 PST ---
I see, you're right.
Specifically one should be able to explicitly default initialize a field.
union { T1 t1; T2 t2 = T2.init; }

NB: A workaround to the aforementioned bug is to simply change the order of
union fields so that the one with explicit initializer comes first.

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--- Comment #3 from Kenji Hara k.hara...@gmail.com 2013-10-01 07:16:17 PDT ---
(In reply to comment #1)
 Another variation:
 
 union S
 {
 float[2] a;
 struct
 {
 union { float i = 1; float x; }
 union { float j = 2; float y; }
 }
 }
 
 $ dmd bar.d -c
 bar.d(2): Error: union bar.S overlapping initialization for struct S.i
 bar.d(2): Error: union bar.S overlapping initialization for struct S.j
 
 If 'a' is moved below the anonymous struct it works. The spec does not mention
 this special case as far as I can tell. Explicit initialization of aggregate
 fields inside anonymous struct/union combinations should be documented.

More reduced test case.

union U1
{
int a = 1;  // OK
string b;
}
union U2
{
int a;
string b = s;  // overlapping initialization for struct U2.b
}

I discovered this behavior while debugging other compiler bug. If there's
overlapped fields, and the non-first field is explicitly initialized, compiler
rejects it by overlapping initialization.

As far as I see, the behavior seems to be intended by the current compiler
code. However, normally D language semantics does not rely on the lexical order
of declarations. I can agree that the behavior is contrary to the basic
principle.

---

I'd propose more better semantics:

If exactly one field has an explicit initializer between overlapped fields,
compiler should prefer it for default initialization.

U1 u1;  assert(u1.a == 1);
U2 u2;  assert(u2.b == s);

If there's no explicitly initialized field between overlapped siblings, the
first one is initialized at the default initialization.

union U3 { int a; char c; }U3 u3;  assert(u3.a == 0);
union U4 { char c; int a; }U4 u4;  assert(u4.c == 0xff);

If two or more fields have explicit initializers between overlapped siblings,
it would cause compilation error.

union U5 { int a = 1, string b = s }
U5 u5;   // Error: overlapped initialization between U5.a and U5.b

How about that?

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Kenji Hara k.hara...@gmail.com changed:

   What|Removed |Added

Version|1.018   |D2


--- Comment #4 from Kenji Hara k.hara...@gmail.com 2013-10-01 07:17:08 PDT ---
Change to D2 issue.

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[Issue 1432] Bogus overlapping initialization error with structs, unions, and member initializers

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Trass3r mrmoc...@gmx.de changed:

   What|Removed |Added

 CC||mrmoc...@gmx.de
   Platform|x86 |All
 OS/Version|Windows |All


--- Comment #2 from Trass3r mrmoc...@gmx.de 2011-11-27 06:08:55 PST ---
The first example compiles fine now.
Really not sure if the second should compile at all, but the order of
compilation dependence is definitely a bug.

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--- Comment #1 from to...@famolsen.dk  2009-04-22 21:33 ---
Another variation:

union S
{
float[2] a;
struct
{
union { float i = 1; float x; }
union { float j = 2; float y; }
}
}

$ dmd bar.d -c
bar.d(2): Error: union bar.S overlapping initialization for struct S.i
bar.d(2): Error: union bar.S overlapping initialization for struct S.j

If 'a' is moved below the anonymous struct it works. The spec does not mention
this special case as far as I can tell. Explicit initialization of aggregate
fields inside anonymous struct/union combinations should be documented.


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