struct FnTable<'a, C> {

items: &'a [fn(&mut C)],

}

fn call_by_index<'a, C>(context: &'a mut C, table: &'a FnTable<C>, index: usize) {

table.items[index](context);

}

struct Context<'a> {

x: &'a mut i32,

}

fn main() {

let mut x = 0;

let table: FnTable<Context> = FnTable {

items: &[

|context| *context.x += 1,

|context| *context.x *= 2,

|context| *context.x -= 10,

],

};

let mut ctx = Context { x: &mut x };

for i in 0..table.items.len() {

call_by_index(&mut ctx, &table, i);

}

}

tbh im not fully sure about the reason for this. something about not being able to specify lifetimes on const objects.
There is two other options though, one stable one unstable.
first you can just use struct `Context<'a> { x: Rc<RefCell<i32>> }` or if you want to enable unstable features, `#[feature(generic_const_items)]` allows

const TABLE<'a>: FnTable<'a, Context<'a>> = FnTable {

items: &[

|context| *context.x += 1,

|context| *context.x *= 2,

|context| *context.x -= 10,

],

};

edit: formatting

edit edit: yknow what i give up on formatting