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digitalmars.D.bugs - [Issue 3551] New: nested struct => dmd adds a hidden pointer

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=3551

           Summary: nested struct => dmd adds a hidden pointer
           Product: D
           Version: 2.036
          Platform: Other
        OS/Version: All
            Status: NEW
          Keywords: wrong-code
          Severity: regression
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: nfxjfg gmail.com


--- Comment #0 from nfxjfg gmail.com 2009-11-25 02:16:13 PST ---
Take this code:

void main() {
    struct X {
        int x;
        int bar() { return x; }
    }
    X s;
}

dmd2 adds a hidden pointer to struct X. That means s.sizeof==8. For extra
buggyness, the hidden pointer appears in s.tupleof.

This silently breaks many uses of structs. Especially it breaks C
compatibility, the bit-layout for asm code, and whatever you think of.

At the very least, dmd should never add a hidden pointer if that hidden pointer
gets is not needed.

Actually, I consider this an anti-feature, because dmd should NEVER add
(non-static) hidden fields to structs. The request to fix or remove this
feature is part of this bug report. The language spec should also be fixed.
Note that even if the hidden pointer is added only if needed, this is still
bug-prone, because it requires complicated semantic analysis just to tell,
whether the struct's size got messed up.

I propose to add a "dynamic" attribute for nested structs. If a struct is
tagged with "dynamic", it can reference variables from its enclosing scope, and
may need a hidden pointer.

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next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=3551


Don <clugdbug yahoo.com.au> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |clugdbug yahoo.com.au


--- Comment #1 from Don <clugdbug yahoo.com.au> 2009-11-25 02:21:53 PST ---
(In reply to comment #0)
 Take this code:
 
 void main() {
     struct X {
         int x;
         int bar() { return x; }
     }
     X s;
 }
 
 dmd2 adds a hidden pointer to struct X. That means s.sizeof==8. For extra
 buggyness, the hidden pointer appears in s.tupleof.
 
 This silently breaks many uses of structs. Especially it breaks C
 compatibility, the bit-layout for asm code, and whatever you think of.
 
 At the very least, dmd should never add a hidden pointer if that hidden pointer
 gets is not needed.
 
 Actually, I consider this an anti-feature, because dmd should NEVER add
 (non-static) hidden fields to structs. The request to fix or remove this
 feature is part of this bug report. The language spec should also be fixed.
 Note that even if the hidden pointer is added only if needed, this is still
 bug-prone, because it requires complicated semantic analysis just to tell,
 whether the struct's size got messed up.
 
 I propose to add a "dynamic" attribute for nested structs. If a struct is
 tagged with "dynamic", it can reference variables from its enclosing scope, and
 may need a hidden pointer.

In the spec, that's what static structs are for. Nested _anything_ has this behaviour. Declare it as a static struct if you don't want the hidden pointer. Please close this bug as invalid, and create a new one: "static nested structs are not implemented". -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Nov 25 2009
prev sibling next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=3551


Walter Bright <bugzilla digitalmars.com> changed:

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


--- Comment #2 from Walter Bright <bugzilla digitalmars.com> 2009-11-30
02:22:08 PST ---
Declaring the struct as static should work, I'll make that fix.

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prev sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=3551


Walter Bright <bugzilla digitalmars.com> changed:

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


--- Comment #3 from Walter Bright <bugzilla digitalmars.com> 2009-12-06
00:55:04 PST ---
Fixed dmd 2.037

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