Problem casting mut ref in call to native function

[boggle]

Passing a v: &mut int to a function in a native module that expects a &mut c_int via a type cast v as &mut c_int yields an internal compiler error

I hit this when rewriting math and am logging this here.

[brson]

Do you have a test case?

[boggle]

Hit this when writing the new lib math in a currently unused function, went for using plain pointers for now.

cf. https://github.com/boggle/rust/blob/libmath/src/libmath/math_impl/generic.rs#L163 which calls https://github.com/boggle/rust/tree/libmath/src/libmath/math_impl#L67

[catamorphism]

This appears to have been fixed fortuitously. I added a test case -- src/test/run-pass/issue-2214.rs -- which I believe tests the same issue, and it passes. Closing.

[nikomatsakis]

So... I am looking at this test now... casting a *int to a *c_int does not seem like a particularly good idea, as int and c_int have different sizes. I guess int is strictly larger than c_int, so this probably works out ok on a little-endian machine, but in general it's not something we want in our libraries.

[boggle]

I thought rust int was defined as == c_int. Have to think about this in terms of math lib.

[nikomatsakis]

No, they are not the same. That's why we give a warning if you use Rust int in the definition of a native function. A rust int is the same as C's intptr_t