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181 lines
5.7 KiB
Rust
181 lines
5.7 KiB
Rust
// run-pass
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#![allow(unused_imports)]
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#![allow(non_snake_case)]
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// ASCII art shape renderer. Demonstrates traits, impls, operator overloading,
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// non-copyable struct, unit testing. To run execute: rustc --test shapes.rs &&
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// ./shapes
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// Rust's std library is tightly bound to the language itself so it is
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// automatically linked in. However the extra library is designed to be
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// optional (for code that must run on constrained environments like embedded
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// devices or special environments like kernel code) so it must be explicitly
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// linked in.
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// Extern mod controls linkage. Use controls the visibility of names to modules
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// that are already linked in. Using WriterUtil allows us to use the write_line
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// method.
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use std::fmt;
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use std::iter::repeat;
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use std::slice;
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// Represents a position on a canvas.
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#[derive(Copy, Clone)]
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struct Point {
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x: isize,
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y: isize,
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}
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// Represents an offset on a canvas. (This has the same structure as a Point.
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// but different semantics).
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#[derive(Copy, Clone)]
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struct Size {
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width: isize,
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height: isize,
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}
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#[derive(Copy, Clone)]
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struct Rect {
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top_left: Point,
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size: Size,
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}
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// Contains the information needed to do shape rendering via ASCII art.
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struct AsciiArt {
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width: usize,
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height: usize,
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fill: char,
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lines: Vec<Vec<char> > ,
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// This struct can be quite large so we'll disable copying: developers need
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// to either pass these structs around via references or move them.
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}
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impl Drop for AsciiArt {
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fn drop(&mut self) {}
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}
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// It's common to define a constructor sort of function to create struct instances.
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// If there is a canonical constructor it is typically named the same as the type.
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// Other constructor sort of functions are typically named from_foo, from_bar, etc.
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fn AsciiArt(width: usize, height: usize, fill: char) -> AsciiArt {
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// Build a vector of vectors containing blank characters for each position in
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// our canvas.
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let lines = vec![vec!['.'; width]; height];
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// Rust code often returns values by omitting the trailing semi-colon
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// instead of using an explicit return statement.
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AsciiArt {width: width, height: height, fill: fill, lines: lines}
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}
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// Methods particular to the AsciiArt struct.
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impl AsciiArt {
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fn add_pt(&mut self, x: isize, y: isize) {
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if x >= 0 && x < self.width as isize {
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if y >= 0 && y < self.height as isize {
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// Note that numeric types don't implicitly convert to each other.
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let v = y as usize;
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let h = x as usize;
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// Vector subscripting will normally copy the element, but &v[i]
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// will return a reference which is what we need because the
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// element is:
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// 1) potentially large
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// 2) needs to be modified
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let row = &mut self.lines[v];
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row[h] = self.fill;
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}
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}
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}
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}
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// Allows AsciiArt to be converted to a string using the libcore ToString trait.
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// Note that the %s fmt! specifier will not call this automatically.
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impl fmt::Display for AsciiArt {
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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// Convert each line into a string.
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let lines = self.lines.iter()
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.map(|line| line.iter().cloned().collect())
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.collect::<Vec<String>>();
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// Concatenate the lines together using a new-line.
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write!(f, "{}", lines.join("\n"))
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}
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}
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// This is similar to an interface in other languages: it defines a protocol which
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// developers can implement for arbitrary concrete types.
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trait Canvas {
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fn add_point(&mut self, shape: Point);
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fn add_rect(&mut self, shape: Rect);
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// Unlike interfaces traits support default implementations.
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// Got an ICE as soon as I added this method.
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fn add_points(&mut self, shapes: &[Point]) {
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for pt in shapes {self.add_point(*pt)};
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}
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}
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// Here we provide an implementation of the Canvas methods for AsciiArt.
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// Other implementations could also be provided (e.g., for PDF or Apple's Quartz)
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// and code can use them polymorphically via the Canvas trait.
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impl Canvas for AsciiArt {
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fn add_point(&mut self, shape: Point) {
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self.add_pt(shape.x, shape.y);
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}
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fn add_rect(&mut self, shape: Rect) {
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// Add the top and bottom lines.
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for x in shape.top_left.x..shape.top_left.x + shape.size.width {
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self.add_pt(x, shape.top_left.y);
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self.add_pt(x, shape.top_left.y + shape.size.height - 1);
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}
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// Add the left and right lines.
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for y in shape.top_left.y..shape.top_left.y + shape.size.height {
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self.add_pt(shape.top_left.x, y);
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self.add_pt(shape.top_left.x + shape.size.width - 1, y);
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}
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}
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}
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// Rust's unit testing framework is currently a bit under-developed so we'll use
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// this little helper.
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pub fn check_strs(actual: &str, expected: &str) -> bool {
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if actual != expected {
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println!("Found:\n{}\nbut expected\n{}", actual, expected);
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return false;
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}
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return true;
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}
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fn test_ascii_art_ctor() {
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let art = AsciiArt(3, 3, '*');
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assert!(check_strs(&art.to_string(), "...\n...\n..."));
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}
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fn test_add_pt() {
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let mut art = AsciiArt(3, 3, '*');
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art.add_pt(0, 0);
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art.add_pt(0, -10);
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art.add_pt(1, 2);
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assert!(check_strs(&art.to_string(), "*..\n...\n.*."));
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}
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fn test_shapes() {
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let mut art = AsciiArt(4, 4, '*');
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art.add_rect(Rect {top_left: Point {x: 0, y: 0}, size: Size {width: 4, height: 4}});
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art.add_point(Point {x: 2, y: 2});
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assert!(check_strs(&art.to_string(), "****\n*..*\n*.**\n****"));
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}
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pub fn main() {
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test_ascii_art_ctor();
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test_add_pt();
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test_shapes();
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}
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