Has someone figured out a reliable way to determine at compile time whether a function parameter is passed by reference or by copy?

The functionality (ParamsPassMethodTuple) in std.bind does not work. (It
expects that giving a const T to a function expecting ref T will fail,
which leads to wrong results for simple types like int.)

Modifying it to check with enum T, invariant T or the type's initializer fails. I noticed that ParameterTypeTuple!(function) contains the ref/out etc. in the tuple, but there seems to be no way to test for it. (stringof aside)

Anyway, I think it's odd that for

void foo(ref int i) {}
void foo2(ParameterTypeTuple!(foo)) {}

ParameterTypeTuple!(foo) is (ref int) and
ParameterTypeTuple!(foo2) is (int).

Regards,
Christian Kamm

Christian Kamm wrote:
> Has someone figured out a reliable way to determine at compile time whether
> a function parameter is passed by reference or by copy?
> 
> The functionality (ParamsPassMethodTuple) in std.bind does not work. (It
> expects that giving a const T to a function expecting ref T will fail,
> which leads to wrong results for simple types like int.) 
> 
> Modifying it to check with enum T, invariant T or the type's initializer
> fails. I noticed that ParameterTypeTuple!(function) contains the ref/out
> etc. in the tuple, but there seems to be no way to test for it. (stringof
> aside)
> 
> Anyway, I think it's odd that for
> 
> void foo(ref int i) {}
> void foo2(ParameterTypeTuple!(foo)) {}
> 
> ParameterTypeTuple!(foo) is (ref int) and
> ParameterTypeTuple!(foo2) is (int).
> 
> Regards,
> Christian Kamm

Looks like a bug

> Christian Kamm wrote:
>> Anyway, I think it's odd that for
>> 
>> void foo(ref int i) {}
>> void foo2(ParameterTypeTuple!(foo)) {}
>> 
>> ParameterTypeTuple!(foo) is (ref int) and
>> ParameterTypeTuple!(foo2) is (int).

Robert Fraser wrote:
> Looks like a bug

I'm not sure. After all it is a type tuple - and ref int isn't a distinct type from int. Also

void foo(ref int i) {}
ParameterTypeTuple!(foo).stringof == "(ref int)"
ParameterTypeTuple!(foo)[0].stringof == "int".

A while back Andrei found it problematic that there is no way to write a function template ident(F) such that foo and ident!(foo) behave exactly the same. It might be the beginnings of a not-yet-done storage class manipulation feature.

For the record, this works for me:

template isRefArg(int i, alias func)
{
    enum isRefArg =
        ParameterTypeTuple!(func)[i..i+1].stringof ==
        ParameterTypeTuple!(
            void delegate(ref ParameterTypeTuple!(func)[i])
          ).stringof;
}

Note that the [i..i+1] leads to the storage class being retained where [i] would discard it.

I have reported some of the behavior as bug 1818: http://d.puremagic.com/issues/show_bug.cgi?id=1818 .

Cheers,
Christian