[Mono-dev] Why is UnmanagedType_80 required?

[Kornél Pál]

>>>>>> According to my experiences using no ArraySubType has the same result
>>>>>> as
>>>>>> ArraySubType = (UnmanagedType)80 on mcs and csc.exe as well.
>>>>>>
>>>>>> Could someone tell me please why UnmanagedType_80 is required?
>>>>>
>>>>>There was a bug in ancient versions of mcs wrt. constant folding in
>>>>>attribute arguments.  We needed to declare an explicit enumeration
>>>>>constant, and use that instead.
>>>>
>>>> I think in this case we could simply eliminate UnmanagedType_80 in
>>>> favour of
>>>> using no ArraySubType as I think we support those ancient versions no
>>>> more.
>>>>
>>>>>The actual reason for using '(UnmanagetType) 80': probably corcompare.
>>>>
>>>> Using no ArraySubType and using ArraySubType = (UnmanagedType)80
>>>> results in
>>>> the same binary file.
>>>
>>> I don't think so.  It will be emitted in the MarshalAsAttribute
>>> metadata.
>>
>> Hmm...  I spoke too soon.  It's a pseudo-attribute.  With no
>> ArraySubType specified, the current mcs compiler code seems to set the
>> element type of the LParray marshaller to 'int' (I4).  ArraySubType set
>> to '80' i.e. MAX, specifies to the marshaller that there's "no info"
>> about the element type.
>>
>> Either way, I think there should be a difference in the metadata.
>
>(Sorry for following up to myself so much :-)
>
>It turns out that this behaviour could be a bug in our compiler.  CSC
>and Mono's SRE appear to behave as you say -- not specifying
>ArraySubType acts the same as specifying (UnmanagedType)80.

I found another difference in ildasm output when using SizeParamIndex as
well. So I'm going to file a bug report with some examples.

When mcs will emit correct metadata when using no ArraySubType can
(UnmanagedType)80 be removed and use no ArraySubType without problems?

Kornél