http://d.puremagic.com/issues/show_bug.cgi?id=3731

           Summary: Immutable class may be changed when inherits from
                    mutable parent
           Product: D
           Version: 2.039
          Platform: x86
        OS/Version: Windows
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody@puremagic.com
        ReportedBy: tomeksowi@gmail.com


--- Comment #0 from Tomasz Sowiński <tomeksowi@gmail.com> 2010-01-20 12:44:48 PST ---
This merrily compiles:

class Zmienna {
    int a;
    this(int a) {
        this.a = a;
    }
}

immutable class Stala : Zmienna {
    this(int a) {
        super(a);
    }
}

void main() {
    auto st = new Stala(5);
    Zmienna zm = st;
    zm.a = 666;
//  st.a = 666; // fails
    assert (st.a == 666);
}


The above shows that an immutable class shouldn't be allowed to derive from mutable classes. Unfortunately it won't work because Object is not (and can't be) immutable. Not sure how to bite this one, perhaps make an opt out that says mutable parents with no fields are OK? Or an exception only for Object?

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Steven Schveighoffer <schveiguy@yahoo.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |schveiguy@yahoo.com


--- Comment #1 from Steven Schveighoffer <schveiguy@yahoo.com> 2010-01-21 05:43:28 PST ---
The solution would be to make it illegal to have a mutable class reference to the base class.

In your example, this line should be an error:

Zmienna zm = st; // error, must use immutable(Zmienna) or const(Zmienna)

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--- Comment #2 from Tomasz Sowiński <tomeksowi@gmail.com> 2010-01-21 11:03:00 PST ---
(In reply to comment #1)
> The solution would be to make it illegal to have a mutable class reference to the base class.
> 
> In your example, this line should be an error:
> 
> Zmienna zm = st; // error, must use immutable(Zmienna) or const(Zmienna)

Thanks, that makes sense.

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yebblies <yebblies@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |accepts-invalid, patch
                 CC|                            |yebblies@gmail.com
            Summary|Immutable class may be      |Can implicitly cast an
                   |changed when inherits from  |immutable reference to a
                   |mutable parent              |derived class


--- Comment #3 from yebblies <yebblies@gmail.com> 2011-06-13 22:59:03 PDT ---
https://github.com/D-Programming-Language/dmd/pull/125

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--- Comment #4 from Kenji Hara <k.hara.pg@gmail.com> 2011-09-16 03:24:37 PDT ---
I think issue 3731 is same as issue 5080, and the yebblies patch is a bit better than mine.

See also Don and Steven's comments in 5080.

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yebblies <yebblies@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rayerd.wiz@gmail.com


--- Comment #5 from yebblies <yebblies@gmail.com> 2011-12-13 16:23:28 EST ---
*** Issue 6863 has been marked as a duplicate of this issue. ***

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--- Comment #6 from github-bugzilla@puremagic.com 2012-01-27 20:24:11 PST ---
Commits pushed to master at https://github.com/D-Programming-Language/phobos

https://github.com/D-Programming-Language/phobos/commit/7bed81961aefc5327b57be0862514b78d84355db
The fix for issue 3731 shows a couple of places in phobos that rely on this
bug.  std.xml is going away, so work around the issue for now (all problems are
caused by opEquals and opCmp not being const correct) and in std.datetime, AA
values must be rebindable.

https://github.com/D-Programming-Language/phobos/commit/472c2a984391a97fd6fda5b77d082e184b828c87 Merge pull request #408 from yebblies/issue3731

Remove implicit casts to mutable super class

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yebblies <yebblies@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |k.hara.pg@gmail.com


--- Comment #7 from yebblies <yebblies@gmail.com> 2012-01-31 13:13:15 EST ---
*** Issue 5080 has been marked as a duplicate of this issue. ***

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dawg@dawgfoto.de changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dawg@dawgfoto.de


--- Comment #8 from dawg@dawgfoto.de 2012-03-04 05:19:41 PST ---
*** Issue 7636 has been marked as a duplicate of this issue. ***

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Stewart Gordon <smjg@iname.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|Can implicitly cast an      |Derived class implicitly
                   |immutable reference to a    |convertible to base class
                   |derived class               |with arbitrary change of
                   |                            |constancy


--- Comment #9 from Stewart Gordon <smjg@iname.com> 2012-03-25 07:52:59 PDT ---
(In reply to comment #1)
> The solution would be to make it illegal to have a mutable class reference to the base class.

No, because a Zmienna is perfectly allowed to be mutable.  It's Stala that isn't.

> In your example, this line should be an error:
> 
> Zmienna zm = st; // error, must use immutable(Zmienna) or const(Zmienna)

Correct, since because Stala is immutable, any object reference of type Stala is actually of type immutable(Stala).

The bug is that constancy is ignored when converting from a derived class to a base class, as this code shows (DMD 2.058, Win32):
----------
class Base           { int x; }
class Derived : Base { int y; }

void main() {
    Derived            md;
    const(Derived)     cd;
    immutable(Derived) id;

    Base               mb_md = md;
    const(Base)        cb_md = md;
    immutable(Base)    ib_md = md; // accepts-invalid

    Base               mb_cd = cd; // accepts-invalid
    const(Base)        cb_cd = cd;
    immutable(Base)    ib_cd = cd; // accepts-invalid

    Base               mb_id = id; // accepts-invalid
    const(Base)        cb_id = id;
    immutable(Base)    ib_id = id;
}

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