I want to implement add trait for a struct which imlpements Fn trait

help
1 
impl<A> Add for PathFunctionStruct<A> where A:PathFunction{
    type Output=PathFunctionStruct<A>;
    fn add(self,other:Self)->Self::Output{
        PathFunctionStruct(|t:Time| {self.0(t)+other.0(t)})
    }
}
pub struct PathFunctionStruct<A>(A) where A:PathFunction;
pub trait PathFunction: Fn(Time) -> Position + Sized {}
impl<T: Fn(Time) -> Position> PathFunction for T {}
pub struct Time(f64);
pub struct Position(f64, f64, f64);
impl Add for Position {
    type Output = Self;
    fn add(self, other: Self) -> Self::Output {
        Position(self.0 + other.0,self.1 + other.1,self.2 + other.2)
    }
}

I am trying to do Structure and Interpretation of Classical Mechanics in rust.
I want to be able to add path functions for particles just by using + sign instead of using add method. Is there a way to do this?
Well a way except using dyn keyword.

Since all closures are technically of different type Add is not working for PathFunctionStruct

2

Instead of trying to get this work with closures, just define a method on your own trait:

pub trait PathFunction {
    fn position_at(time: Time) -> Position;
}

then create concrete types for each desired operation (e.g. Add<F, G>), then implement PathFunction for them. Playground.

Other comments:

  • don't put bounds on struct definitions, it's unnecessary
  • don't call structs XYZStruct. It doesn't matter w.r.t. naming whether a type is a struct or an enum; that's an implementation detail. Name types after their semantics, not their mechanics.
2 Likes
3

Thanks. My method of using simple add function not even the add trait would have also failed because manually implementing Fn traits is not allowed.

4

Actually, if you don't need the Add trait, then the solution is much easier as you can just stick to returning closures and specify the return type as impl FnMut(Time) -> Position (or impl PathFunction). Playground.

5

That is what I am currently doing in my code.

6

This topic was automatically closed 90 days after the last reply. We invite you to open a new topic if you have further questions or comments.