"David Lowndes" <Da****@example.invalidwrote in message
news:6r********************************@4ax.com...
Does the code use pragma warning anywhere?
That particular code was a VS2005 generated C++/CLI console project, I
set W4 in the project settings to see if it would identify an issue -
it didn't :(
I can't see anything in the generated sources that would drop the
warning level.
Dave
Looks like an issue because .NET has no concept of a constant reference.
Part of your problem is that you're accepting a tracking reference. Since
int is a value type, you can use & instead, which works as expected and
generates an error.
void f1(int% ri)
{
ri = 0;
}
void f2(int& ri)
{
ri = 0;
}
int get(void)
{
return 10;
}
int main(void)
{
f1(get()); // no error
f2(get()); // error
}
However, the documentation says that % should work as well (See article: How
to: Write Template Functions that Take Native, Value, or Reference
Parameters), so this looks like a genuine bug. I think we should look at
the generated MSIL, I suspect that implicit boxing is taking place.
..method assembly static int32 main() cil managed
{
.maxstack 1
.locals (
[0] int32 num1)
L_0000: call int32 <Module>::get()
L_0005: stloc.0
L_0006: ldloca.s num1
L_0008: call void <Module>::f1(int32&)
L_000d: ldc.i4.0
L_000e: ret
}
Nope, no boxing. Just a temporary passed by non-const reference. Seems to
be a result of Microsoft's choice not to implement const safety in managed
code. There's no way the compiler can know from the function prototype
whether the argument will be changed. Seems like it should then be a
warning instead of an error.
However, even adding the OutAttribute on the parameter, the code doesn't
generate even a warning although it clearly should be an error to use a
temporary as an out-only parameter.
File a bug report and I'll vote for and validate it, here's your minimal
repro code (compile with /clr:safe):
void f1([System::Runtime::InteropServices::Out] int% ri)
{
ri = 0;
}
int get( void )
{
return 10;
}
int main(void)
{
f1(get());
}
