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digitalmars.D.bugs - [Issue 4977] New: cannot use nothrow or pure with Rebindable

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=4977

           Summary: cannot use nothrow or pure with Rebindable
           Product: D
           Version: unspecified
          Platform: Other
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Phobos
        AssignedTo: nobody puremagic.com
        ReportedBy: jmdavisProg gmx.com


--- Comment #0 from Jonathan M Davis <jmdavisProg gmx.com> 2010-10-02 17:39:46
PDT ---
Rebindable does nothing about nothrow or pure. None of its functions are marked
on nothrow or pure, making it rather difficult to use Rebindable with a type
which has carefully been made to correctly use nothrow and/or pure.

The first thing would be to make opDot() nothrow and pure. I'm pretty sure that
you can get away with that (though pure may not be possible until the next
version of the compiler is released with the changes to pure that Don
suggested).

opAssign() would probably be just as easy, though I'm not sure. Since we're
dealing with copying classes, interfaces, or arrays, I think that you can just
make opAssign nothrow with no problem (since you have no postblit constructor
to worry about possibly throwing). On purity, I'm not so sure. It might work
now, or it might require the changes Don suggested, but I think that it will
work at that point.

Since the constructor uses opAssign(), it will probably be just as
easy/difficult to change as opAssign will be.

In any case, as it stands, its rather difficult to use either nothrow or pure
with Rebindable, which either severely limits where you can use Rebindable, or
it severely limits the type that you put in Rebindable.

rebindable() will likely have to be changed appropriately as well.

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--- Comment #1 from Jonathan M Davis <jmdavisProg gmx.com> 2010-10-02 18:25:53
PDT ---
It looks like opDot() doesn't work with const or immutable Rebindable!()'s. So,
it probably needs a second version which is const (and possible a third for
immutable) in order to work with them. Otherwise, const member functions don't
work very well with member variables which are Rebindable!().

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--- Comment #2 from Jonathan M Davis <jmdavisProg gmx.com> 2010-10-02 18:39:56
PDT ---
Here's a first attempt at a solution:

Rebindable(T) if (is(T == class) || is(T == interface) || isArray!(T))
{
    static if (!is(T X == const(U), U) && !is(T X == immutable(U), U))
    {
        alias T Rebindable;
    }
    else static if (isArray!(T))
    {
        alias const(ElementType!(T))[] Rebindable;
    }
    else
    {
        struct Rebindable
        {
            private union
            {
                T original;
                U stripped;
            }

            void opAssign(T another) nothrow
            {
                stripped = cast(U) another;
            }

            void opAssign(Rebindable another) nothrow
            {
                stripped = another.stripped;
            }

            static if (is(T == const U))
            {
                // safely assign immutable to const
                void opAssign(Rebindable!(immutable U) another) nothrow
                {
                    stripped = another.stripped;
                }
            }

            this(T initializer) nothrow
            {
                opAssign(initializer);
            }

             property T get() const pure nothrow
            {
                return original;
            }

            T opDot() pure nothrow
            {
                return original;
            }

            T opDot() const pure nothrow
            {
                return original;
            }
        }
    }
}


With the current purity rules, I can't make opAssign() pure. It complains about
assigning to const. I don't know whether or nat that will be fixed with the
relaxed purity rules suggested by Don.

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--- Comment #3 from Jonathan M Davis <jmdavisProg gmx.com> 2010-10-02 19:53:51
PDT ---
With the fix for bug # 3318, the new get property function now joins opDot() in
needing a const version with both versions being nothrow.

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

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


--- Comment #4 from Kenji Hara <k.hara.pg gmail.com> 2011-08-23 20:28:07 PDT ---
https://github.com/D-Programming-Language/phobos/pull/213

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prev sibling parent d-bugmail puremagic.com writes:
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Kenji Hara <k.hara.pg gmail.com> changed:

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


--- Comment #5 from Kenji Hara <k.hara.pg gmail.com> 2011-09-06 03:05:22 PDT ---
https://github.com/D-Programming-Language/phobos/commit/936f2a4c38dcca8cfe0a7e4247bddcff2f19f8ba

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