Memoization of closure

[EdwardRaff]

Hi, I'm new to Rust - sorry if this is dumb, but I'm not finding a solution.

I have a function that is passed in and user-controlled, and it must be that way. My code will use that function extensively, and in some cases, will re-call the function with the same arguments many times.

The code would be much cleaner if I could memoize the input function, which would mean memoizing a closure that captures the input function. But this code:

    #[memoize]
    let dist_cached = |a: &usize, b: &usize| -> f32{
        return my_dist(a, b);
    };

Does not work.

Is there a way to do or support this kind of operation?

[dermesser]

no, that's not supported - memoize only works on free-standing functions. But at this point, it's maybe not the right choice anyway; it's not too hard to build a custom approach using your favored map, eviction policy, and so on.

[EdwardRaff]

I would have thought so, but my scenario looks something like:

//user calling to library 
let my_dist = |a: &usize, b &usize| {
     //calculate
}
fn outer(&my_dist) { 
    let struct_with_members = ///
    struct_with_members.functionThatCallsManyRepeats(&my_dist /*other arguments*/); 
}

and I've not been able to get the Rust compiler to let me do this. If I do a new closure in outer it yels about functionThatCallsManyRepeats not being a Fn and that the closure is a FnMut. When I change functionThatCallsManyRepeats to take a FnMut, then the compiler errors that at FnMut is expected bu instead received a closure.

Sorry, I can't share more code; this is a work item.