https://issues.dlang.org/show_bug.cgi?id=12885
Issue 12885 depends on issue 12883, which changed state.

Issue 12883 Summary: implicit conversion of struct to mutable via alias this https://issues.dlang.org/show_bug.cgi?id=12883

           What    |Removed                     |Added
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             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |INVALID

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https://issues.dlang.org/show_bug.cgi?id=12885

Nils <nilsbossung@googlemail.com> changed:

           What    |Removed                     |Added
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             Status|ASSIGNED                    |NEW
           Assignee|nilsbossung@googlemail.com  |nobody@puremagic.com

--- Comment #1 from Nils <nilsbossung@googlemail.com> ---
As issue 12883 has been closed as invalid, I don't have a plan how to go about this. Unassigning from me.

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https://issues.dlang.org/show_bug.cgi?id=12885

Andrei Alexandrescu <andrei@erdani.com> changed:

           What    |Removed                     |Added
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                 CC|                            |andrei@erdani.com

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https://issues.dlang.org/show_bug.cgi?id=12885

FeepingCreature <default_357-line@yahoo.de> changed:

           What    |Removed                     |Added
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                 CC|                            |default_357-line@yahoo.de
           Severity|enhancement                 |normal

--- Comment #2 from FeepingCreature <default_357-line@yahoo.de> ---
I just ran into this. This bug breaks std.json quite badly: see https://issues.dlang.org/show_bug.cgi?id=19256 , in which const(JSONValue) implicitly converts to JSONValue, allowing us to mutate JSON objects via a const parameter.

This is definitely unacceptable.

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https://issues.dlang.org/show_bug.cgi?id=12885

Martin Nowak <code@dawg.eu> changed:

           What    |Removed                     |Added
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                 CC|                            |code@dawg.eu

--- Comment #3 from Martin Nowak <code@dawg.eu> ---
I don't fully agree with the reasoning in issue 11257.
It seems like casts could be used to bypass const checks for implementations of
Rebindable et.al.

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https://issues.dlang.org/show_bug.cgi?id=12885
Issue 12885 depends on issue 12883, which changed state.

Issue 12883 Summary: implicit conversion of struct to mutable via alias this https://issues.dlang.org/show_bug.cgi?id=12883

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
         Resolution|INVALID                     |---

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https://issues.dlang.org/show_bug.cgi?id=12885

Walter Bright <bugzilla@digitalmars.com> changed:

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

--- Comment #4 from Walter Bright <bugzilla@digitalmars.com> ---
Martin is right.

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https://issues.dlang.org/show_bug.cgi?id=12885

--- Comment #5 from Walter Bright <bugzilla@digitalmars.com> ---
https://github.com/dlang/dmd/pull/9061

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https://issues.dlang.org/show_bug.cgi?id=12885

Walter Bright <bugzilla@digitalmars.com> changed:

           What    |Removed                     |Added
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           See Also|                            |https://issues.dlang.org/sh
                   |                            |ow_bug.cgi?id=12883,
                   |                            |https://issues.dlang.org/sh
                   |                            |ow_bug.cgi?id=19256,
                   |                            |https://issues.dlang.org/sh
                   |                            |ow_bug.cgi?id=11257

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https://issues.dlang.org/show_bug.cgi?id=12885

Steven Schveighoffer <schveiguy@gmail.com> changed:

           What    |Removed                     |Added
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                 CC|                            |schveiguy@gmail.com

--- Comment #6 from Steven Schveighoffer <schveiguy@gmail.com> ---
I just ran into this, with vibe.d Json type. Well, not a problem exactly, I just noticed I happened to be stripping const by accident, and it alarmed me that the compiler lets you get away with it.

I will note that this fails:

```d
union U
{
   int *p;
   int i;
}
void main()
{
   const U c;
   U m = c;
}
```

I see no reason why this should fail but the other should not, the inconsistency itself is a problem.

But beyond that, I will note that a struct that contains such an overlapping is convertible from const to mutable in @safe code. This in itself isn't a problem since you can't access the pointer value in @safe code. But surely if you wanted to provide access for @safe callers (like, for a tagged union, like Json), there would be trusted escapes, and those would surely not expect an implicit conversion of a const pointer to a mutable pointer.

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