Question about return types from .map() about rayon HOT 4 CLOSED

I don't understand the question. Are you getting errors from this? Are the return types not what you intended?

from rayon.

Hello,

Apologies for my unclear question. I am not getting errors, but you are right that my return types are not what I expected.

The first function returns a tuple of vectors, while the second function returns a vector of tuples. I am not sure why function 1 would return a different type than function 2 given the underlying functions that are being mapped.

from rayon.

The collect() method is generic, where its return type can be anything that implements FromParallelIterator, and that is usually inferred from the surrounding context. So in the first case:

let (azimuth_series, zenith_series) = (/*iter*/).collect();

Your let pattern is forcing the result to be a tuple, and you must have some other code that is driving type inference for each of those "series" to end up fully resolved as (Vec<T>, Vec<U>). Rayon has an implementation of FromParallelIterator for tuple pairs that acts pretty much like unzip().

In the second case, your code is explicitly forcing the Vec<(X, Y, Z)> type for collect():

let spherical_coordinates: Vec<(SunCartesianX, SunCartesianY, SunCartesianZ)> = (/*iter*/).collect();

We don't have a direct way to collect (Vec<X>, Vec<Y>, Vec<Z>), if that's what you wanted, but you can use nested tuple pairs for this if you produce parallel items of the same shape, like:

let (vx, (vy, vz)) = (/* iter with Item=(x, (y, z)) */).collect();
// or
let ((vx, vy), vz) = (/* iter with Item=((x, y), z) */).collect();

from rayon.

Thank you! That was a very clear explanation. Closing as complete.

from rayon.