[Mono-bugs] [Bug 32269][Nor] Changed - Cast from enum variable to System.Enum gives null
15 Oct 2002 00:29:04 -0000
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Changed by firstname.lastname@example.org.
--- shadow/32269 Mon Oct 14 14:05:45 2002
+++ shadow/32269.tmp.8449 Mon Oct 14 20:29:04 2002
@@ -1,14 +1,14 @@
@@ -45,6 +45,40 @@
Actually, it's the cast from MyEnum to System.Enum gives null on mono.
However, I've left the code snippet exactly as it was when I tested it on a
windows box at work today, so I'm sure of the behaviour on windows.
+------- Additional Comments From email@example.com 2002-10-14 20:29 -------
+For what it's worth (and it might not be worth much), here are my
+1) This seems related to 31835
+2) The fix for 31835 seems to cause the test case this bug report to
+fail to even compile (error CS0029: Cannot convert implicitly from
+`object' to `System.Enum') (but I think mcs is closer to correctness
+with the 31835 fix than without it)
+What appears to be happening is that the line
+ System.Enum se = (System.Enum) me;
+causes variable me to be boxed (the explicit conversion code first
+tries to do an implicit conversion of "me" to System.Enum, which hits
+the code for for bug 31835 and boxes it). Boxing creates an instance
+of type object. Assignment to variable se (of type System.Enum) from
+type object is not allowed. Hence the error.
+Therefore, a possible fix is to augment the fix for 31835 so that,
+when necessary, it does a ClassCast of the BoxedCast instead of just
+the BoxedCast -- it seems to work on the limited tests I've done.
+The odd thing is that csc is quite happy to box and store to "se"
+without emitting the classcast instruction, which looks incorrect to
+me, unless you assume that boxing does more than what the C# spec
+says: return "the resulting instance as a value of type object". If
+mcs were to implement this behaviour, I suspect BoxedCast would need
+to be modified...
+Hope that this commentary is useful to whoever works on this...
+Hopefully it is even correct :)