Can't declare static fns in multiple anonymous implementations

[erickt]

Some static functions may only make sense for certain constrained typarams, but this is disallowed. For example:

type A<T> = ~[T];

impl<T> A<T> {
    static fn new() -> A<T> { ~[] }
}

impl<T: Copy> A<T> {
    static fn new_copyable() -> A<T> { ~[] }
}

fn main() {}

However, rust errors with this message:

test.rs:7:0: 9:1 error: duplicate definition of type A
test.rs:7 impl<T: Copy> A<T> {
test.rs:8     static fn new_copyable() -> A<T> { ~[] }
test.rs:9 }
test.rs:3:0: 5:1 note: first definition of type A here:
test.rs:3 impl<T> A<T> {
test.rs:4     static fn new() -> A<T> { ~[] }
test.rs:5 }
error: aborting due to previous error

[catamorphism]

Not critical for 0.6 (and possibly a wontfix but I haven't read carefully enough); de-milestoning.

[catamorphism]

I think we're not going to support this.

[erickt]

@catamorphism said I could reopen this. It's not a priority, but I feel it'd be handy.

[thestinger]

Use case: two constructors for std::rc::{Rc, RcMut}, one for Owned and one for Const. Right now they have to be free functions.

[huonw]

This would be useful for extra::complex, specifically, to close #5734 by having a separate impl like:

impl<T: Trignometric> Cmplx<T> {
     fn from_polar(r: T, arg: T) -> Cmplx<T> { .. }
     fn to_polar(&self) -> (T,T) { .. }
}

rather than needlessly requiring all types used with Cmplx have sin and cos defined by lumping this into the impl with the generic new.

[brendanzab]

yeah I hit this too: https://gist.github.com/bjz/7ccf949e65e361863cd2 :(

Use case:

impl<T> Vec4<T> {
    #[inline(always)]
    fn new(x: T, y: T, z: T, w: T) -> Vec4<T> {
        Vec4 { x: x, y: y, z: z, w: w }
    }

    #[inline(always)]
    fn len() -> uint { 4 }

    //...
}

impl<T:Copy + Num> Vec4<T> {
    #[inline(always)]
    fn identity() -> Vec4<T> {
        Vec4::new(One::one::<T>(), One::one::<T>(), One::one::<T>(), One::one::<T>())
    }

    #[inline(always)]
    fn zero() -> Vec4<T> {
        Vec4::new(Zero::zero::<T>(), Zero::zero::<T>(), Zero::zero::<T>(), Zero::zero::<T>())
    }

    //...
}

Specifically because I would like to be able to to return a Vec4 (like in GLSL) for component-wise vector comparisons.

[luqmana]

Fixed by #7029