[Mono-list] How to pass an object as ref or out

[Robert Jordan]

On 17.04.2014 18:33, Robert Jordan wrote:
> On 17.04.2014 16:55, carmack2000 wrote:
>> After I followed your code I got this error:
>> Unhandled exception at 0x100b8c87 in MonoScriptingTest.exe: 0xC0000005:
>> Access violation reading location 0x00000000.
>> I'll look into this.
>>
>> You said 'This is no better than the former non-ref version.' If I
>> want to
>> use ref-object to return values (GetPosition), how can I get it ?
>>
>> C#
>> [MethodImplAttribute(MethodImplOptions.InternalCall)]
>> public static extern void GetPosition(string name, ref Vector2 o)
>>
>> C++: still doing like this ?
>> void GetPosition(MonoString* ms, MonoObject** mo)
>> {
>>          Vector2 pos = *(Vector2*)mono_object_unbox(*mo);
>>          pos.x = xxxx; // Returned to the caller
>>          pos.y = xxxx;
>> }
>
> void GetPosition(MonoString* ms, Vector2 *vector)
> {
>      vector->x = ...
> }
>
> It assumes that you have a C/C++ Vector2 declaration
> that is fully layout-compatible with the managed version.
>
> Robert

Additionally, to make this work Vector2 must be a value type,
but it seems to be one because otherwise you won't call
mono_object_unbox on it.

However, the thread's subject might imply that the above code
were suitable for object arguments. Of course it's not,
so caveat emptor.


Robert