http://d.puremagic.com/issues/show_bug.cgi?id=6288

           Summary: std.conv.to removes const/immutable when converting a
                    class
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Phobos
        AssignedTo: nobody@puremagic.com
        ReportedBy: schveiguy@yahoo.com


--- Comment #0 from Steven Schveighoffer <schveiguy@yahoo.com> 2011-07-11 10:19:14 PDT ---
The code in std.conv.to looks like this for converting to base/derived class:

/**
Object-to-object conversions throw exception when the source is
non-null and the target is null.
 */
T toImpl(T, S)(S value) if (is(S : Object) && is(T : Object))
{
    auto result = cast(T) value;
    if (!result && value)
    {
        throw new ConvException("Cannot convert object of static type "
                ~S.classinfo.name~" and dynamic type "~value.classinfo.name
                ~" to type "~T.classinfo.name);
    }
    return result;
}

This does not take into account that cast can easily remove const or immutable decorations.

For example:

import std.conv;

class C {}
class D : C {}

void main()
{
    const(C) c = new D;
    D d = to!D(c);
    assert(d !is null);
}

This compiles as of 2.054, and clearly is removing const without requiring a cast.

Unfortunately, cast() is the mechanism to do dynamic conversions, so the logic to allow compilation needs to check that const is not being removed or immutable is not being removed/added.

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |patch


--- Comment #1 from Kenji Hara <k.hara.pg@gmail.com> 2011-09-20 05:44:35 PDT ---
https://github.com/D-Programming-Language/phobos/pull/271

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Steven Schveighoffer <schveiguy@yahoo.com> changed:

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


--- Comment #2 from Steven Schveighoffer <schveiguy@yahoo.com> 2011-09-22 08:00:36 PDT ---
https://github.com/D-Programming-Language/phobos/commit/8b6ef3b46be8ea50b9aef96b2b2d12c378315189

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |Jesse.K.Phillips+D@gmail.co
                   |                            |m


--- Comment #3 from Kenji Hara <k.hara.pg@gmail.com> 2011-10-09 03:47:02 PDT ---
*** Issue 5307 has been marked as a duplicate of this issue. ***

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