# Objective
Make `StableInterpolate` "just work" on tuples whose parts are each
`StableInterpolate` types. These types arise notably through
`Curve::zip` (or just through explicit mapping of a similar form). It
would otherwise be kind of frustrating to stumble upon such a thing and
then realize that, e.g., automatic resampling just doesn't work, even
though there is a very "obvious" way to do it.
## Solution
Infer `StableInterpolate` on tuples of up to size 11. I can make that
number bigger, if desired. Unfortunately, I don't think that our
standard "fake variadics" tools actually work for this; the anonymous
field accessors of tuples are `:tt` for purposes of macro expansion,
which means that you can't simplify away the identifiers by doing
something clever like using recursion (which would work if they were
`:expr`). Maybe someone who knows some incredibly dark magic could chime
in with a better solution.
The expanded impls look like this:
```rust
impl<
T0: StableInterpolate,
T1: StableInterpolate,
T2: StableInterpolate,
T3: StableInterpolate,
T4: StableInterpolate,
> StableInterpolate for (T0, T1, T2, T3, T4)
{
fn interpolate_stable(&self, other: &Self, t: f32) -> Self {
(
<T0 as StableInterpolate>::interpolate_stable(&self.0, &other.0, t),
<T1 as StableInterpolate>::interpolate_stable(&self.1, &other.1, t),
<T2 as StableInterpolate>::interpolate_stable(&self.2, &other.2, t),
<T3 as StableInterpolate>::interpolate_stable(&self.3, &other.3, t),
<T4 as StableInterpolate>::interpolate_stable(&self.4, &other.4, t),
)
}
}
```
## Testing
Expanded macros; it compiles.
## Future
Make a version of the fake variadics workflow that supports this kind of
thing.
a09104b62c