[Issue 12118] Modify immutable data using throw

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=12118

Nick Treleaven <nick at geany.org> changed:

           What    |Removed                     |Added
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                 CC|                            |nick at geany.org

--- Comment #5 from Nick Treleaven <nick at geany.org> ---
comment #0:
> It is possible to throw an immutable Exception and catch it as mutable

Also, the exception is mutated when thrown so that is another safety violation
if immutable:
https://github.com/dlang/dmd/blob/v2.101.1/druntime/src/rt/deh.d#L13-L21

comment #3:
> At least, defining immutable constructor in derived classes of Throwable should be disallowed.

That wouldn't disallow:

throw new immutable Exception("");

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