Closed
Description
Working on an example app and got an ICE as soon as I added a default method (add_points).
// ASCII art shape renderer.
// Demonstrates traits, impls, operator overloading, non-copyable struct, unit testing.
// To run execute: rustc --test shapes.rs && ./shapes
// Rust's core library is tightly bound to the language itself so it is automatically linked in.
// However the std library is designed to be optional (for code that must run on constrained
// environments like embedded devices or special environments like kernel code) so it must
// be explicitly linked in.
extern mod std;
// Extern mod controls linkage. Use controls the visibility of names to modules that are
// already linked in. Using WriterUtil allows us to use the write_line method.
use io::WriterUtil;
// Represents a position on a canvas.
struct Point
{
x: int,
y: int,
}
// Represents an offset on a canvas. (This has the same structure as a Point.
// but different semantics).
struct Size
{
width: int,
height: int,
}
struct Rect
{
top_left: Point,
size: Size,
}
// TODO: operators
// Contains the information needed to do shape rendering via ASCII art.
struct AsciiArt
{
width: uint,
height: uint,
priv fill: char,
priv lines: ~[~[mut char]],
// This struct can be quite large so we'll disable copying: developers need
// to either pass these structs around via borrowed pointers or move them.
drop {}
}
// It's common to define a constructor sort of function to create struct instances.
// If there is a canonical constructor it is typically named the same as the type.
// Other constructor sort of functions are typically named from_foo, from_bar, etc.
fn AsciiArt(width: uint, height: uint, fill: char) -> AsciiArt
{
// Use an anonymous function to build a vector of vectors containing
// blank characters for each position in our canvas.
let lines = do vec::build_sized(height)
|push|
{
for height.times
{
let mut line = ~[mut];
vec::grow_set(line, width-1, '.', '.');
push(line);
}
};
// Rust code often returns values by omitting the trailing semi-colon
// instead of using an explicit return statement.
AsciiArt {width: width, height: height, fill: fill, lines: lines}
}
// Methods particular to the AsciiArt struct.
impl AsciiArt
{
fn add_pt(x: int, y: int)
{
if x >= 0 && x < self.width as int
{
if y >= 0 && y < self.height as int
{
// Note that numeric types don't implicitly convert to each other.
let v = y as uint;
let h = x as uint;
// Vector subscripting will normally copy the element, but &v[i]
// will return a reference which is what we need because the
// element is:
// 1) potentially large
// 2) needs to be modified
let row = &self.lines[v];
row[h] = self.fill;
}
}
}
}
// Allows AsciiArt to be converted to a string using the libcore ToStr trait.
// Note that the %s fmt! specifier will not call this automatically.
impl AsciiArt : ToStr
{
fn to_str() -> ~str
{
// Convert each line into a string.
let lines = do self.lines.map |line| {str::from_chars(line)};
// Concatenate the lines together using a new-line.
str::connect(lines, "\n")
}
}
// This is similar to an interface in other languages: it defines a protocol which
// developers can implement for arbitrary concrete types.
trait Canvas
{
fn add_point(shape: Point);
fn add_rect(shape: Rect);
// Unlike interfaces traits support default implementations.
// Got an ICE as soon as I added this method.
fn add_points(shapes: &[Point])
{
for shapes.each |pt| {self.add_point(pt)};
}
}
// Here we provide an implementation of the Canvas methods for AsciiArt.
// Other implementations could also be provided (e.g. for PDF or Apple's Quartz)
// and code can use them polymorphically via the Canvas trait.
impl AsciiArt : Canvas
{
fn add_point(shape: Point)
{
self.add_pt(shape.x, shape.y);
}
fn add_rect(shape: Rect)
{
// Add the top and bottom lines.
for int::range(shape.top_left.x, shape.top_left.x + shape.size.width)
|x|
{
self.add_pt(x, shape.top_left.y);
self.add_pt(x, shape.top_left.y + shape.size.height - 1);
}
// Add the left and right lines.
for int::range(shape.top_left.y, shape.top_left.y + shape.size.height)
|y|
{
self.add_pt(shape.top_left.x, y);
self.add_pt(shape.top_left.x + shape.size.width - 1, y);
}
}
}
// Rust's unit testing framework is currently a bit under-developed so we'll use
// this little helper.
pub fn check_strs(actual: &str, expected: &str) -> bool
{
if actual != expected
{
io::stderr().write_line(fmt!("Found:\n%s\nbut expected\n%s", actual, expected));
return false;
}
return true;
}
#[test]
fn test_ascii_art_ctor()
{
let art = AsciiArt(3, 3, '*');
assert check_strs(art.to_str(), "...\n...\n...");
}
#[test]
fn test_add_pt()
{
let art = AsciiArt(3, 3, '*');
art.add_pt(0, 0);
art.add_pt(0, -10);
art.add_pt(1, 2);
assert check_strs(art.to_str(), "*..\n...\n.*.");
}
#[test]
fn test_shapes()
{
let art = AsciiArt(4, 4, '*');
art.add_rect(Rect {top_left: Point {x: 0, y: 0}, size: Size {width: 4, height: 4}});
art.add_point(Point {x: 2, y: 2});
assert check_strs(art.to_str(), "****\n*..*\n*.**\n****");
}
This is with rust from Sep 22, 2012.