Tuple support

[andreiltd]

Would you be willing to pull the patch that adds support for tuples? It looks like the code is good to go and it is only a matter of adding impl_trait!((T, T)) for each type and then testing it.

I wouldn't go deep with the size of tuples and only implement pairs which I think is the most common case.

[sdroege]

Unfortunately the memory layout for tuples is not defined. While in practice e.g. a (u8, u8) is the same memory layout as [u8; 2] this is in no way guaranteed (and also the order in which it is stored in memory might be different) and can break in future Rust versions unless it is defined at some point.

[andreiltd]

I see, then there is no way to implement that reliably for now. Thanks for the explanation.

[sdroege]

This could be fixed by submitting a Rust RFC that defines that the memory layout of homogeneous tuples is equivalent to the corresponding array. I don't think there's any practical reason to not define it like that other than nobody having spent time on that yet.

[andreiltd]

rust-lang/unsafe-code-guidelines#36

[sdroege]

The support for primitive arrays from #18 can kind of help here. Instead of working with e.g. (f32, f32) you could work with [f32; 2].