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Add trait object example

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This commit is contained in:
Timothy Warren 2019-02-06 14:28:09 -05:00
parent ec147dce21
commit bac5c02bd8
6 changed files with 187 additions and 85 deletions
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2
.idea/misc.xml
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@ -32,6 +32,8 @@
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9
.idea/rust.iml
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@ -130,6 +130,13 @@
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@ -142,6 +149,7 @@
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@ -159,6 +167,7 @@
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170
.idea/workspace.xml
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@ -13,21 +13,7 @@
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@ -263,6 +252,16 @@
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@ -272,18 +271,15 @@
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@ -311,13 +307,15 @@
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7
gui/Cargo.toml Normal file
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@ -0,0 +1,7 @@
[package]
name = "gui"
version = "0.1.0"
authors = ["Timothy Warren <twarren@nabancard.com>"]
edition = "2018"
[dependencies]

48
gui/src/lib.rs Normal file
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@ -0,0 +1,48 @@
//! An implementation of a "trait object",
//! which allows dynamic dispatch for implementing types,
//! even allowing disparate types to be called, unlike a
//! generic, which requires one specific implementation.
//!
//! Trait objects have some limitations (They must be "object-safe"):
//! * Methods can not return `Self`
//! * Methods can not have generic type parameters
/// The base trait definition
pub trait Draw {
fn draw(&self);
}
/// A struct able to utilize the "trait object", via the Box<dyn Draw> type
pub struct Screen {
pub components: Vec<Box<dyn Draw>>,
}
/// A method able to call the draw method on any objects
/// implementing the Draw "trait object"
impl Screen {
pub fn run(&self) {
for component in self.components.iter() {
component.draw();
}
}
}
pub struct Button {
pub width: u32,
pub height: u32,
pub label: String,
}
impl Draw for Button {
fn draw(&self) {
// code to actually draw a button
}
}
#[cfg(test)]
mod tests {
#[test]
fn it_works() {
assert_eq!(2 + 2, 4);
}
}

36
gui/src/main.rs Normal file
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@ -0,0 +1,36 @@
use gui::{Button, Draw, Screen};
struct SelectBox {
width: u32,
height: u32,
options: Vec<String>,
}
impl Draw for SelectBox {
fn draw(&self) {
// code to actually draw a select box
}
}
fn main() {
let screen = Screen {
components: vec![
Box::new(SelectBox {
width: 75,
height: 10,
options: vec![
String::from("Yes"),
String::from("Maybe"),
String::from("No")
],
}),
Box::new(Button {
width: 50,
height: 10,
label: String::from("OK"),
}),
],
};
screen.run();
}