Lifetime problem using into_dyn() to parametrically return markers of various types

[ebardie]

From the docs I believe the function in the attached snapshot is more or less along the correct lines, but as you can see, the compiler isn't happy with TriangleMarker or Cross, cases, but the Circle variant is apparently fine.

The docs (for TriangleMarker and Cross) have:

impl<'a, Coord: 'a, Size: SizeDesc> PointCollection<'a, Coord> for &'a TriangleMarker<Coord, Size>
impl<'a, Coord: 'a, Size: SizeDesc> PointCollection<'a, Coord> for &'a Cross<Coord, Size>

but then drop the lifetime on the Coord generic specifier (for Circle):

impl<'a, Coord, Size: SizeDesc> PointCollection<'a, Coord> for &'a Circle<Coord, Size>

Is this discrepancy causing or related to my issue? How can I work around this?

[ebardie]

Current workaround is to use identical function bodies for two distinct more concrete function prototypes:

pub fn get_marker_i32<'a, DB: DrawingBackend>(coord: (i32, i32), colour: RGBColor, marker: &MarkerType) -> DynElement<'a, DB, (i32, i32)>

and:

pub fn get_marker_db<'a, DB: DrawingBackend>(coord: (DateTime<Utc>, f64), colour: RGBColor, marker: &MarkerType) -> DynElement<'a, DB, (DateTime<Utc>, f64)>

which isn't nice, but at least it gets me going for now.