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digitalmars.D.bugs - [Issue 8098] New: Inner class method can modify outer's members regardless of constancy

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=8098

           Summary: Inner class method can modify outer's members
                    regardless of constancy
           Product: D
           Version: D2
          Platform: x86
        OS/Version: Windows
            Status: NEW
          Keywords: accepts-invalid
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: smjg iname.com
            Blocks: 2573


--- Comment #0 from Stewart Gordon <smjg iname.com> 2012-05-15 07:30:06 PDT ---
class Outer {
    int i = 6;

    class Inner {
        int y=0;

        int foo() const {
            pragma(msg, "this.outer: " ~ typeof(this.outer).stringof);
            pragma(msg, "i:          " ~ typeof(i).stringof);
            return ++i;
        }
    }
    Inner inner;
    this() {
        inner = new Inner;
    }
} 

void main() {
    const(Outer) x = new Outer;
    pragma(msg, "x:          " ~ typeof(x).stringof);
    pragma(msg, "x.inner:    " ~ typeof(x.inner).stringof);
    x.inner.foo();
    writeln(x.i);
}
----------
C:\Users\Stewart\Documents\Programming\D\Tests>dmd inner_const.d
this.outer: const(Outer)
i:          const(int)
x:          const(Outer)
x.inner:    const(Inner)

C:\Users\Stewart\Documents\Programming\D\Tests>inner_const
7
----------
(DMD 2.059 Win32)

x is a const reference.  By transitivity, x.inner is.  So far, so good.

Outer.Inner.foo is a const method.  The call fails if it isn't.  So far, so
good.

From foo's point of view, this.outer and i are reported as const.  So far, so
good.

But despite i being const, it allows it to be modified!

Changing the declaration of x to

    const(Outer) x = new const(Outer);
    const(Outer) x = new immutable(Outer);
    immutable(Outer) x = new immutable(Outer);

makes no difference to the bug.

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--- Comment #1 from Stewart Gordon <smjg iname.com> 2012-05-15 07:47:50 PDT ---
An inner class holds a hidden member that is a reference to the object of the
outer class to which it belongs.  By transitivity, if inner is const or
immutable, then outer must be likewise from inner's point of view.

This implies that an immutable inner can only belong to an immutable outer, and
a const inner can belong to a mutable, const or immutable outer, but inner will
always view the outer as const.

At the moment there doesn't seem to be a way to explicitly set the constancy of
Inner.outer.  But if there were, it would enable a mutable inner to belong to
an outer of any constancy while ensuring const-safety (though the outer class
might not be able to hold a reference to the inner object).

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Kenji Hara <k.hara.pg gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |pull
           Platform|x86                         |All
         OS/Version|Windows                     |All


--- Comment #2 from Kenji Hara <k.hara.pg gmail.com> 2012-05-24 08:20:46 PDT ---
https://github.com/D-Programming-Language/dmd/pull/964

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--- Comment #3 from github-bugzilla puremagic.com 2012-05-24 21:13:49 PDT ---
Commits pushed to master at https://github.com/D-Programming-Language/dmd

https://github.com/D-Programming-Language/dmd/commit/de20f7f9e50c468fe7758604058d0af6bc7f36aa
fix Issue 8098 - Inner class method can modify outer's members regardless of
constancy

https://github.com/D-Programming-Language/dmd/commit/db915a16aba1db00a5ea59f96ad0b0deea7152b5
Merge pull request #964 from 9rnsr/fix8098

Issue 8098 - Inner class method can modify outer's members regardless of
constancy

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Walter Bright <bugzilla digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |bugzilla digitalmars.com
         Resolution|                            |FIXED


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