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// all controls must implement this
trait Control: Sized {
    fn size_x(&self) -> u32;
 
    fn size_y(&self) -> u32;
 
    fn size(&self) -> (u32, u32) {
        return (self.size_x(), self.size_y());
    }
}
 
// all checkboxes must implement this
trait Checkbox: Control {
    fn checked(&self) -> bool;
    fn set_checked(&mut self, is_checked: bool);
}
 
// our custom checkbox has a few supported shapes
#[derive(PartialEq, Copy, Clone)]
enum Shape {
    Circle,
    Square,
    Octagon,
}
 
// and methods to set and retrieve the current shape
trait CustomCheckbox: Checkbox {
    fn shape(&self) -> Shape;
    fn set_shape(&mut self, shape: Shape);
}
 
// this is our custom checkbox control's in-memory representation
struct CoolCheckbox {
    is_checked: bool,
    checkbox_shape: Shape,
    width: u32,
    height: u32,
}
 
impl CoolCheckbox {
    fn new() -> CoolCheckbox {
        CoolCheckbox {
            is_checked: false,
            checkbox_shape: Shape::Square,
            width: 25,
            height: 30,
        }
    }
 
    fn coolness_factor(&self) -> u32 {
        42
    }
}
 
impl Control for CoolCheckbox {
    fn size_x(&self) -> u32 {
        self.width
    }
    fn size_y(&self) -> u32 {
        self.height
    }
}
 
impl Checkbox for CoolCheckbox {
    fn checked(&self) -> bool {
        self.is_checked
    }
    fn set_checked(&mut self, is_checked: bool) {
        self.is_checked = is_checked
    }
}
 
impl CustomCheckbox for CoolCheckbox {
    fn shape(&self) -> Shape {
        self.checkbox_shape
    }
 
    fn set_shape(&mut self, shape: Shape) {
        self.checkbox_shape = shape;
    }
}
 
// doesn't care what kind of control it is
fn do_general<ControlT>(control: &ControlT) -> u32
where
    ControlT: Control,
{
    control.size_x() * control.size_y()
}
 
// doesn't need to know that it is your custom checkbox
fn do_something<CheckboxT>(checkbox: &CheckboxT) -> bool
where
    CheckboxT: Checkbox,
{
    let size_x = checkbox.size_x();
    let checked = checkbox.checked();
 
    //returns true if checkbox is wide enough and checked... for whatever reason
    size_x > 40 && checked
}
 
// only works on checkboxes that implement CustomCheckbox
fn do_something_specifc<CheckboxT>(checkbox: &CheckboxT) -> &''static str
where
    CheckboxT: CustomCheckbox,
{
    let size_x = checkbox.size_x();
    let checked = checkbox.checked();
    let shape = checkbox.shape();
 
    //returns true if checkbox is wide enough and checked... for whatever reason
    if shape == Shape::Circle && size_x > 40 && checked {
        "this CustomCheckbox rocks"
    } else {
        "this CustomCheckbox is only a little awesome"
    }
}
 
// only works for our concrete implementation of CoolCheckbox
fn do_coolcheckbox_stuff(coolbox: &CoolCheckbox) -> u32 {
    coolbox.coolness_factor() + 5
}
 
fn main() {
    let mycheckbox = CoolCheckbox::new();
 
    println!("general: {}", do_general(&mycheckbox));
    println!("checkbox: {}", do_something(&mycheckbox));
    println!("customcheckbox: {}", do_something_specifc(&mycheckbox));
    println!("coolcheckbox: {}", do_coolcheckbox_stuff(&mycheckbox));
}