Current objects (~) #224
Description
In Dyon you need a stack reference to mutate arrays with push(mut,_) and pop(mut). This does not work very well with deep object hierarchies, because it does a copy-on-write when there is more than one reference to a variable on the heap. This encourages programmers to use data-oriented programming style, where you iterate over arrays.
A normal application requires many flat structures, and you end up with long function names like this:
fn render_dlist_world_bullets_comets(mut dlist, world, bullets, comets) { ... }By using current objects, you can reduce the length of function names and the amount of typing:
// Uses current objects `dlist`, `world`, `bullets`, `comets`.
fn render_world() ~ mut dlist, world, bullets, comets { ... }Syntax
To declare a new current object, one uses ~ in front of the variable name:
fn main() {
// The `~` sign make these current objects for the scope of called functions.
~ window := new_window(title: "hello world!")
~ bullets := init_bullets()
~ comets := init_comets()
loop {
if !next_event(mut window) { break }
...
set(title: "start the game!")
...
update_world(dt)
}
}To use current objects, you put ~ and a list of variables after function arguments:
fn set_title(title: str) ~ mut window {
// Set the title of the current window.
set(window: window, title: title)
}
fn update_world(dt) ~ mut bullets, mut comets {
// Move objects.
move(bullets, dt)
move(comets, dt)
...
}
fn move(mut objects, dt) {
for i { objects[i][0] += dt * objects[i][1] }
}Motivation
These rules are designed for
- Make refactoring easier
- Improve readability
- Reduce typing