[Issue 6316] New: Class downcast is rejected in @safe code

[Issue 6316] Regression(2.054): Class downcast is rejected in @safe code

Jul 14, 2011

yebblies

Jul 15, 2011

Walter Bright

July 14, 2011

[Issue 6316] New: Class downcast is rejected in @safe code

Posted by Harry Vennik

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Harry Vennik

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http://d.puremagic.com/issues/show_bug.cgi?id=6316

           Summary: Class downcast is rejected in @safe code
           Product: D
           Version: D2
          Platform: x86
        OS/Version: Mac OS X
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody@puremagic.com
        ReportedBy: htvennik@gmail.com


--- Comment #0 from Harry Vennik <htvennik@gmail.com> 2011-07-14 06:30:27 PDT ---
The D language specification does not forbid downcasting in @safe code, but the compiler rejects it. Downcasting is actually safe because such casts are checked run-time.

The minimal testcase is:

------- CODE -------
class A { }
class B : A { }

@safe void main()
{
    A a = new A();
    B b = cast(B) a;
}
----- END CODE -----


The above code is rejected by the compiler with the following message: safe_downcast.d(7): Error: cast from safe_downcast.A to safe_downcast.B not allowed in safe code



Possible enhancement: make DMD issue a warning if the result of a downcast is not checked for null.

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http://d.puremagic.com/issues/show_bug.cgi?id=6316 kennytm@gmail.com changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |kennytm@gmail.com --- Comment #1 from kennytm@gmail.com 2011-07-14 06:46:17 PDT --- You should use std.conv.to, and then in Phobos the toImpl specialization T toImpl(T, S)(S value) if (!isImplicitlyConvertible!(S, T) && is(S : Object) && !is(typeof(value.opCast!T()) : T) && is(T : Object) && !is(typeof(new T(value)))) should be made @trusted. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------

http://d.puremagic.com/issues/show_bug.cgi?id=6316 yebblies <yebblies@gmail.com> changed: What |Removed |Added ---------------------------------------------------------------------------- Keywords| |patch, rejects-valid CC| |yebblies@gmail.com Platform|x86 |All Summary|Class downcast is rejected |Regression(2.054): Class |in @safe code |downcast is rejected in | |@safe code OS/Version|Mac OS X |All --- Comment #2 from yebblies <yebblies@gmail.com> 2011-07-15 00:16:42 EST --- https://github.com/D-Programming-Language/dmd/pull/252 -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------

http://d.puremagic.com/issues/show_bug.cgi?id=6316 Walter Bright <bugzilla@digitalmars.com> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|NEW |RESOLVED CC| |bugzilla@digitalmars.com Resolution| |FIXED --- Comment #3 from Walter Bright <bugzilla@digitalmars.com> 2011-07-15 16:19:42 PDT --- https://github.com/D-Programming-Language/dmd/commit/48b8cee356ef3b3681df26129d7b3f4d9dd9d34c -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------

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